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clang-p2996/llvm/test/Transforms/LoopUnroll/runtime-loop-at-most-two-exits.ll
Philip Reames 37ead201e6 [runtime-unroll] Use incrementing IVs instead of decrementing ones 
This is one of those wonderful "in theory X doesn't matter, but in practice is does" changes. In this particular case, we shift the IVs inserted by the runtime unroller to clamp iteration count of the loops* from decrementing to incrementing.

Why does this matter?  A couple of reasons:
* SCEV doesn't have a native subtract node.  Instead, all subtracts (A - B) are represented as A + -1 * B and drops any flags invalidated by such.  As a result, SCEV is slightly less good at reasoning about edge cases involving decrementing addrecs than incrementing ones.  (You can see this in the inferred flags in some of the test cases.)
* Other parts of the optimizer produce incrementing IVs, and they're common in idiomatic source language.  We do have support for reversing IVs, but in general if we produce one of each, the pair will persist surprisingly far through the optimizer before being coalesced.  (You can see this looking at nearby phis in the test cases.)

Note that if the hardware prefers decrementing (i.e. zero tested) loops, LSR should convert back immediately before codegen.

* Mostly irrelevant detail: The main loop of the prolog case is handled independently and will simple use the original IV with a changed start value.  We could in theory use this scheme for all iteration clamping, but that's a larger and more invasive change.
2021-11-12 15:44:58 -08:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -loop-unroll -unroll-runtime=true -unroll-runtime-epilog=true -unroll-runtime-other-exit-predictable=true -verify-loop-lcssa -verify-dom-info -verify-loop-info -S | FileCheck %s --check-prefix=ENABLED
; RUN: opt < %s -loop-unroll -unroll-runtime=true -unroll-runtime-epilog=true -unroll-runtime-other-exit-predictable=false -verify-loop-lcssa -verify-dom-info -verify-loop-info -S | FileCheck %s --check-prefix=DISABLED
define i32 @test(i32* nocapture %a, i64 %n) {
; ENABLED-LABEL: @test(
; ENABLED-NEXT: entry:
; ENABLED-NEXT: [[TMP0:%.*]] = add i64 [[N:%.*]], -1
; ENABLED-NEXT: [[XTRAITER:%.*]] = and i64 [[N]], 7
; ENABLED-NEXT: [[TMP1:%.*]] = icmp ult i64 [[TMP0]], 7
; ENABLED-NEXT: br i1 [[TMP1]], label [[FOR_END_UNR_LCSSA:%.*]], label [[ENTRY_NEW:%.*]]
; ENABLED: entry.new:
; ENABLED-NEXT: [[UNROLL_ITER:%.*]] = sub i64 [[N]], [[XTRAITER]]
; ENABLED-NEXT: br label [[HEADER:%.*]]
; ENABLED: header:
; ENABLED-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ 0, [[ENTRY_NEW]] ], [ [[INDVARS_IV_NEXT_7:%.*]], [[FOR_BODY_7:%.*]] ]
; ENABLED-NEXT: [[SUM_02:%.*]] = phi i32 [ 0, [[ENTRY_NEW]] ], [ [[ADD_7:%.*]], [[FOR_BODY_7]] ]
; ENABLED-NEXT: [[NITER:%.*]] = phi i64 [ 0, [[ENTRY_NEW]] ], [ [[NITER_NEXT_7:%.*]], [[FOR_BODY_7]] ]
; ENABLED-NEXT: [[CMP:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP]], label [[FOR_EXIT2_LOOPEXIT:%.*]], label [[FOR_BODY:%.*]]
; ENABLED: for.body:
; ENABLED-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, i32* [[A:%.*]], i64 [[INDVARS_IV]]
; ENABLED-NEXT: [[TMP2:%.*]] = load i32, i32* [[ARRAYIDX]], align 4
; ENABLED-NEXT: [[ADD:%.*]] = add nsw i32 [[TMP2]], [[SUM_02]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT:%.*]] = add nuw nsw i64 [[INDVARS_IV]], 1
; ENABLED-NEXT: [[NITER_NEXT:%.*]] = add nuw nsw i64 [[NITER]], 1
; ENABLED-NEXT: [[CMP_1:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_1]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_1:%.*]]
; ENABLED: for.body.1:
; ENABLED-NEXT: [[ARRAYIDX_1:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT]]
; ENABLED-NEXT: [[TMP3:%.*]] = load i32, i32* [[ARRAYIDX_1]], align 4
; ENABLED-NEXT: [[ADD_1:%.*]] = add nsw i32 [[TMP3]], [[ADD]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_1:%.*]] = add nuw nsw i64 [[INDVARS_IV_NEXT]], 1
; ENABLED-NEXT: [[NITER_NEXT_1:%.*]] = add nuw nsw i64 [[NITER_NEXT]], 1
; ENABLED-NEXT: [[CMP_2:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_2]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_2:%.*]]
; ENABLED: for.body.2:
; ENABLED-NEXT: [[ARRAYIDX_2:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT_1]]
; ENABLED-NEXT: [[TMP4:%.*]] = load i32, i32* [[ARRAYIDX_2]], align 4
; ENABLED-NEXT: [[ADD_2:%.*]] = add nsw i32 [[TMP4]], [[ADD_1]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_2:%.*]] = add nuw nsw i64 [[INDVARS_IV_NEXT_1]], 1
; ENABLED-NEXT: [[NITER_NEXT_2:%.*]] = add nuw nsw i64 [[NITER_NEXT_1]], 1
; ENABLED-NEXT: [[CMP_3:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_3]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_3:%.*]]
; ENABLED: for.body.3:
; ENABLED-NEXT: [[ARRAYIDX_3:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT_2]]
; ENABLED-NEXT: [[TMP5:%.*]] = load i32, i32* [[ARRAYIDX_3]], align 4
; ENABLED-NEXT: [[ADD_3:%.*]] = add nsw i32 [[TMP5]], [[ADD_2]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_3:%.*]] = add nuw nsw i64 [[INDVARS_IV_NEXT_2]], 1
; ENABLED-NEXT: [[NITER_NEXT_3:%.*]] = add nuw nsw i64 [[NITER_NEXT_2]], 1
; ENABLED-NEXT: [[CMP_4:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_4]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_4:%.*]]
; ENABLED: for.body.4:
; ENABLED-NEXT: [[ARRAYIDX_4:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT_3]]
; ENABLED-NEXT: [[TMP6:%.*]] = load i32, i32* [[ARRAYIDX_4]], align 4
; ENABLED-NEXT: [[ADD_4:%.*]] = add nsw i32 [[TMP6]], [[ADD_3]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_4:%.*]] = add nuw nsw i64 [[INDVARS_IV_NEXT_3]], 1
; ENABLED-NEXT: [[NITER_NEXT_4:%.*]] = add nuw nsw i64 [[NITER_NEXT_3]], 1
; ENABLED-NEXT: [[CMP_5:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_5]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_5:%.*]]
; ENABLED: for.body.5:
; ENABLED-NEXT: [[ARRAYIDX_5:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT_4]]
; ENABLED-NEXT: [[TMP7:%.*]] = load i32, i32* [[ARRAYIDX_5]], align 4
; ENABLED-NEXT: [[ADD_5:%.*]] = add nsw i32 [[TMP7]], [[ADD_4]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_5:%.*]] = add nuw nsw i64 [[INDVARS_IV_NEXT_4]], 1
; ENABLED-NEXT: [[NITER_NEXT_5:%.*]] = add nuw nsw i64 [[NITER_NEXT_4]], 1
; ENABLED-NEXT: [[CMP_6:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_6]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_6:%.*]]
; ENABLED: for.body.6:
; ENABLED-NEXT: [[ARRAYIDX_6:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT_5]]
; ENABLED-NEXT: [[TMP8:%.*]] = load i32, i32* [[ARRAYIDX_6]], align 4
; ENABLED-NEXT: [[ADD_6:%.*]] = add nsw i32 [[TMP8]], [[ADD_5]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_6:%.*]] = add nuw nsw i64 [[INDVARS_IV_NEXT_5]], 1
; ENABLED-NEXT: [[NITER_NEXT_6:%.*]] = add nuw nsw i64 [[NITER_NEXT_5]], 1
; ENABLED-NEXT: [[CMP_7:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_7]], label [[FOR_EXIT2_LOOPEXIT]], label [[FOR_BODY_7]]
; ENABLED: for.body.7:
; ENABLED-NEXT: [[ARRAYIDX_7:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_NEXT_6]]
; ENABLED-NEXT: [[TMP9:%.*]] = load i32, i32* [[ARRAYIDX_7]], align 4
; ENABLED-NEXT: [[ADD_7]] = add nsw i32 [[TMP9]], [[ADD_6]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_7]] = add i64 [[INDVARS_IV_NEXT_6]], 1
; ENABLED-NEXT: [[NITER_NEXT_7]] = add i64 [[NITER_NEXT_6]], 1
; ENABLED-NEXT: [[NITER_NCMP_7:%.*]] = icmp eq i64 [[NITER_NEXT_7]], [[UNROLL_ITER]]
; ENABLED-NEXT: br i1 [[NITER_NCMP_7]], label [[FOR_END_UNR_LCSSA_LOOPEXIT:%.*]], label [[HEADER]]
; ENABLED: for.end.unr-lcssa.loopexit:
; ENABLED-NEXT: [[SUM_0_LCSSA_PH_PH:%.*]] = phi i32 [ [[ADD_7]], [[FOR_BODY_7]] ]
; ENABLED-NEXT: [[INDVARS_IV_UNR_PH:%.*]] = phi i64 [ [[INDVARS_IV_NEXT_7]], [[FOR_BODY_7]] ]
; ENABLED-NEXT: [[SUM_02_UNR_PH:%.*]] = phi i32 [ [[ADD_7]], [[FOR_BODY_7]] ]
; ENABLED-NEXT: br label [[FOR_END_UNR_LCSSA]]
; ENABLED: for.end.unr-lcssa:
; ENABLED-NEXT: [[SUM_0_LCSSA_PH:%.*]] = phi i32 [ undef, [[ENTRY:%.*]] ], [ [[SUM_0_LCSSA_PH_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
; ENABLED-NEXT: [[INDVARS_IV_UNR:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[INDVARS_IV_UNR_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
; ENABLED-NEXT: [[SUM_02_UNR:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[SUM_02_UNR_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
; ENABLED-NEXT: [[LCMP_MOD:%.*]] = icmp ne i64 [[XTRAITER]], 0
; ENABLED-NEXT: br i1 [[LCMP_MOD]], label [[HEADER_EPIL_PREHEADER:%.*]], label [[FOR_END:%.*]]
; ENABLED: header.epil.preheader:
; ENABLED-NEXT: br label [[HEADER_EPIL:%.*]]
; ENABLED: header.epil:
; ENABLED-NEXT: [[INDVARS_IV_EPIL:%.*]] = phi i64 [ [[INDVARS_IV_NEXT_EPIL:%.*]], [[FOR_BODY_EPIL:%.*]] ], [ [[INDVARS_IV_UNR]], [[HEADER_EPIL_PREHEADER]] ]
; ENABLED-NEXT: [[SUM_02_EPIL:%.*]] = phi i32 [ [[ADD_EPIL:%.*]], [[FOR_BODY_EPIL]] ], [ [[SUM_02_UNR]], [[HEADER_EPIL_PREHEADER]] ]
; ENABLED-NEXT: [[EPIL_ITER:%.*]] = phi i64 [ 0, [[HEADER_EPIL_PREHEADER]] ], [ [[EPIL_ITER_NEXT:%.*]], [[FOR_BODY_EPIL]] ]
; ENABLED-NEXT: [[CMP_EPIL:%.*]] = icmp eq i64 [[N]], 42
; ENABLED-NEXT: br i1 [[CMP_EPIL]], label [[FOR_EXIT2_LOOPEXIT2:%.*]], label [[FOR_BODY_EPIL]]
; ENABLED: for.body.epil:
; ENABLED-NEXT: [[ARRAYIDX_EPIL:%.*]] = getelementptr inbounds i32, i32* [[A]], i64 [[INDVARS_IV_EPIL]]
; ENABLED-NEXT: [[TMP10:%.*]] = load i32, i32* [[ARRAYIDX_EPIL]], align 4
; ENABLED-NEXT: [[ADD_EPIL]] = add nsw i32 [[TMP10]], [[SUM_02_EPIL]]
; ENABLED-NEXT: [[INDVARS_IV_NEXT_EPIL]] = add i64 [[INDVARS_IV_EPIL]], 1
; ENABLED-NEXT: [[EXITCOND_EPIL:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT_EPIL]], [[N]]
; ENABLED-NEXT: [[EPIL_ITER_NEXT]] = add i64 [[EPIL_ITER]], 1
; ENABLED-NEXT: [[EPIL_ITER_CMP:%.*]] = icmp ne i64 [[EPIL_ITER_NEXT]], [[XTRAITER]]
; ENABLED-NEXT: br i1 [[EPIL_ITER_CMP]], label [[HEADER_EPIL]], label [[FOR_END_EPILOG_LCSSA:%.*]], !llvm.loop [[LOOP0:![0-9]+]]
; ENABLED: for.end.epilog-lcssa:
; ENABLED-NEXT: [[SUM_0_LCSSA_PH1:%.*]] = phi i32 [ [[ADD_EPIL]], [[FOR_BODY_EPIL]] ]
; ENABLED-NEXT: br label [[FOR_END]]
; ENABLED: for.end:
; ENABLED-NEXT: [[SUM_0_LCSSA:%.*]] = phi i32 [ [[SUM_0_LCSSA_PH]], [[FOR_END_UNR_LCSSA]] ], [ [[SUM_0_LCSSA_PH1]], [[FOR_END_EPILOG_LCSSA]] ]
; ENABLED-NEXT: ret i32 [[SUM_0_LCSSA]]
; ENABLED: for.exit2.loopexit:
; ENABLED-NEXT: [[RETVAL_PH:%.*]] = phi i32 [ [[SUM_02]], [[HEADER]] ], [ [[ADD]], [[FOR_BODY]] ], [ [[ADD_1]], [[FOR_BODY_1]] ], [ [[ADD_2]], [[FOR_BODY_2]] ], [ [[ADD_3]], [[FOR_BODY_3]] ], [ [[ADD_4]], [[FOR_BODY_4]] ], [ [[ADD_5]], [[FOR_BODY_5]] ], [ [[ADD_6]], [[FOR_BODY_6]] ]
; ENABLED-NEXT: br label [[FOR_EXIT2:%.*]]
; ENABLED: for.exit2.loopexit2:
; ENABLED-NEXT: [[RETVAL_PH3:%.*]] = phi i32 [ [[SUM_02_EPIL]], [[HEADER_EPIL]] ]
; ENABLED-NEXT: br label [[FOR_EXIT2]]
; ENABLED: for.exit2:
; ENABLED-NEXT: [[RETVAL:%.*]] = phi i32 [ [[RETVAL_PH]], [[FOR_EXIT2_LOOPEXIT]] ], [ [[RETVAL_PH3]], [[FOR_EXIT2_LOOPEXIT2]] ]
; ENABLED-NEXT: ret i32 [[RETVAL]]
;
; DISABLED-LABEL: @test(
; DISABLED-NEXT: entry:
; DISABLED-NEXT: br label [[HEADER:%.*]]
; DISABLED: header:
; DISABLED-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY:%.*]] ], [ 0, [[ENTRY:%.*]] ]
; DISABLED-NEXT: [[SUM_02:%.*]] = phi i32 [ [[ADD:%.*]], [[FOR_BODY]] ], [ 0, [[ENTRY]] ]
; DISABLED-NEXT: [[CMP:%.*]] = icmp eq i64 [[N:%.*]], 42
; DISABLED-NEXT: br i1 [[CMP]], label [[FOR_EXIT2:%.*]], label [[FOR_BODY]]
; DISABLED: for.body:
; DISABLED-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, i32* [[A:%.*]], i64 [[INDVARS_IV]]
; DISABLED-NEXT: [[TMP0:%.*]] = load i32, i32* [[ARRAYIDX]], align 4
; DISABLED-NEXT: [[ADD]] = add nsw i32 [[TMP0]], [[SUM_02]]
; DISABLED-NEXT: [[INDVARS_IV_NEXT]] = add i64 [[INDVARS_IV]], 1
; DISABLED-NEXT: [[EXITCOND:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[N]]
; DISABLED-NEXT: br i1 [[EXITCOND]], label [[FOR_END:%.*]], label [[HEADER]]
; DISABLED: for.end:
; DISABLED-NEXT: [[SUM_0_LCSSA:%.*]] = phi i32 [ [[ADD]], [[FOR_BODY]] ]
; DISABLED-NEXT: ret i32 [[SUM_0_LCSSA]]
; DISABLED: for.exit2:
; DISABLED-NEXT: [[RETVAL:%.*]] = phi i32 [ [[SUM_02]], [[HEADER]] ]
; DISABLED-NEXT: ret i32 [[RETVAL]]
;
entry:
br label %header
header:
%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
%sum.02 = phi i32 [ %add, %for.body ], [ 0, %entry ]
%cmp = icmp eq i64 %n, 42
br i1 %cmp, label %for.exit2, label %for.body
for.body:
%arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
%0 = load i32, i32* %arrayidx, align 4
%add = add nsw i32 %0, %sum.02
%indvars.iv.next = add i64 %indvars.iv, 1
%exitcond = icmp eq i64 %indvars.iv.next, %n
br i1 %exitcond, label %for.end, label %header
for.end:
%sum.0.lcssa = phi i32 [ %add, %for.body ]
ret i32 %sum.0.lcssa
for.exit2:
%retval = phi i32 [ %sum.02, %header ]
ret i32 %retval
}
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