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clang-p2996/llvm/test/Transforms/LoopVectorize/X86/imprecise-through-phis.ll
Florian Hahn 23c2f2e6b2 [LV] Mark increment of main vector loop induction variable as NUW. 
This patch marks the induction increment of the main induction variable
of the vector loop as NUW when not folding the tail.

If the tail is not folded, we know that End - Start >= Step (either
statically or through the minimum iteration checks). We also know that both
Start % Step == 0 and End % Step == 0. We exit the vector loop if %IV +
%Step == %End. Hence we must exit the loop before %IV + %Step unsigned
overflows and we can mark the induction increment as NUW.

This should make SCEV return more precise bounds for the created vector
loops, used by later optimizations, like late unrolling.

At the moment quite a few tests still need to be updated, but before
doing so I'd like to get initial feedback to make sure I am not missing
anything.

Note that this could probably be further improved by using information
from the original IV.

Attempt of modeling of the assumption in Alive2:
https://alive2.llvm.org/ce/z/H_DL_g

Part of a set of fixes required for PR50412.

Reviewed By: mkazantsev

Differential Revision: https://reviews.llvm.org/D103255
2021-06-07 10:47:52 +01:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -loop-vectorize -mtriple=x86_64-apple-darwin %s | FileCheck %s --check-prefixes=CHECK,SSE
; RUN: opt -S -loop-vectorize -mtriple=x86_64-apple-darwin -mattr=+avx %s | FileCheck %s --check-prefixes=CHECK,AVX
; Two mostly identical functions. The only difference is the presence of
; fast-math flags on the second. The loop is a pretty simple reduction:
; for (int i = 0; i < 32; ++i)
; if (arr[i] != 42)
; tot += arr[i];
define double @sumIfScalar(double* nocapture readonly %arr) {
; CHECK-LABEL: @sumIfScalar(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[I_NEXT:%.*]], [[NEXT_ITER:%.*]] ]
; CHECK-NEXT: [[TOT:%.*]] = phi double [ 0.000000e+00, [[ENTRY]] ], [ [[TOT_NEXT:%.*]], [[NEXT_ITER]] ]
; CHECK-NEXT: [[ADDR:%.*]] = getelementptr double, double* [[ARR:%.*]], i32 [[I]]
; CHECK-NEXT: [[NEXTVAL:%.*]] = load double, double* [[ADDR]], align 8
; CHECK-NEXT: [[TST:%.*]] = fcmp une double [[NEXTVAL]], 4.200000e+01
; CHECK-NEXT: br i1 [[TST]], label [[DO_ADD:%.*]], label [[NO_ADD:%.*]]
; CHECK: do.add:
; CHECK-NEXT: [[TOT_NEW:%.*]] = fadd double [[TOT]], [[NEXTVAL]]
; CHECK-NEXT: br label [[NEXT_ITER]]
; CHECK: no.add:
; CHECK-NEXT: br label [[NEXT_ITER]]
; CHECK: next.iter:
; CHECK-NEXT: [[TOT_NEXT]] = phi double [ [[TOT]], [[NO_ADD]] ], [ [[TOT_NEW]], [[DO_ADD]] ]
; CHECK-NEXT: [[I_NEXT]] = add i32 [[I]], 1
; CHECK-NEXT: [[AGAIN:%.*]] = icmp ult i32 [[I_NEXT]], 32
; CHECK-NEXT: br i1 [[AGAIN]], label [[LOOP]], label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[TOT_NEXT_LCSSA:%.*]] = phi double [ [[TOT_NEXT]], [[NEXT_ITER]] ]
; CHECK-NEXT: ret double [[TOT_NEXT_LCSSA]]
;
entry:
br label %loop
loop:
%i = phi i32 [0, %entry], [%i.next, %next.iter]
%tot = phi double [0.0, %entry], [%tot.next, %next.iter]
%addr = getelementptr double, double* %arr, i32 %i
%nextval = load double, double* %addr
%tst = fcmp une double %nextval, 42.0
br i1 %tst, label %do.add, label %no.add
do.add:
%tot.new = fadd double %tot, %nextval
br label %next.iter
no.add:
br label %next.iter
next.iter:
%tot.next = phi double [%tot, %no.add], [%tot.new, %do.add]
%i.next = add i32 %i, 1
%again = icmp ult i32 %i.next, 32
br i1 %again, label %loop, label %done
done:
ret double %tot.next
}
define double @sumIfVector(double* nocapture readonly %arr) {
; SSE-LABEL: @sumIfVector(
; SSE-NEXT: entry:
; SSE-NEXT: br label [[LOOP:%.*]]
; SSE: loop:
; SSE-NEXT: [[I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[I_NEXT:%.*]], [[NEXT_ITER:%.*]] ]
; SSE-NEXT: [[TOT:%.*]] = phi double [ 0.000000e+00, [[ENTRY]] ], [ [[TOT_NEXT:%.*]], [[NEXT_ITER]] ]
; SSE-NEXT: [[ADDR:%.*]] = getelementptr double, double* [[ARR:%.*]], i32 [[I]]
; SSE-NEXT: [[NEXTVAL:%.*]] = load double, double* [[ADDR]], align 8
; SSE-NEXT: [[TST:%.*]] = fcmp fast une double [[NEXTVAL]], 4.200000e+01
; SSE-NEXT: br i1 [[TST]], label [[DO_ADD:%.*]], label [[NO_ADD:%.*]]
; SSE: do.add:
; SSE-NEXT: [[TOT_NEW:%.*]] = fadd fast double [[TOT]], [[NEXTVAL]]
; SSE-NEXT: br label [[NEXT_ITER]]
; SSE: no.add:
; SSE-NEXT: br label [[NEXT_ITER]]
; SSE: next.iter:
; SSE-NEXT: [[TOT_NEXT]] = phi double [ [[TOT]], [[NO_ADD]] ], [ [[TOT_NEW]], [[DO_ADD]] ]
; SSE-NEXT: [[I_NEXT]] = add i32 [[I]], 1
; SSE-NEXT: [[AGAIN:%.*]] = icmp ult i32 [[I_NEXT]], 32
; SSE-NEXT: br i1 [[AGAIN]], label [[LOOP]], label [[DONE:%.*]]
; SSE: done:
; SSE-NEXT: [[TOT_NEXT_LCSSA:%.*]] = phi double [ [[TOT_NEXT]], [[NEXT_ITER]] ]
; SSE-NEXT: ret double [[TOT_NEXT_LCSSA]]
;
; AVX-LABEL: @sumIfVector(
; AVX-NEXT: entry:
; AVX-NEXT: br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
; AVX: vector.ph:
; AVX-NEXT: br label [[VECTOR_BODY:%.*]]
; AVX: vector.body:
; AVX-NEXT: [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
; AVX-NEXT: [[VEC_PHI:%.*]] = phi <4 x double> [ zeroinitializer, [[VECTOR_PH]] ], [ [[PREDPHI:%.*]], [[VECTOR_BODY]] ]
; AVX-NEXT: [[TMP0:%.*]] = add i32 [[INDEX]], 0
; AVX-NEXT: [[TMP1:%.*]] = getelementptr double, double* [[ARR:%.*]], i32 [[TMP0]]
; AVX-NEXT: [[TMP2:%.*]] = getelementptr double, double* [[TMP1]], i32 0
; AVX-NEXT: [[TMP3:%.*]] = bitcast double* [[TMP2]] to <4 x double>*
; AVX-NEXT: [[WIDE_LOAD:%.*]] = load <4 x double>, <4 x double>* [[TMP3]], align 8
; AVX-NEXT: [[TMP4:%.*]] = fcmp fast une <4 x double> [[WIDE_LOAD]], <double 4.200000e+01, double 4.200000e+01, double 4.200000e+01, double 4.200000e+01>
; AVX-NEXT: [[TMP5:%.*]] = fadd fast <4 x double> [[VEC_PHI]], [[WIDE_LOAD]]
; AVX-NEXT: [[TMP6:%.*]] = xor <4 x i1> [[TMP4]], <i1 true, i1 true, i1 true, i1 true>
; AVX-NEXT: [[PREDPHI]] = select <4 x i1> [[TMP4]], <4 x double> [[TMP5]], <4 x double> [[VEC_PHI]]
; AVX-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4
; AVX-NEXT: [[TMP7:%.*]] = icmp eq i32 [[INDEX_NEXT]], 32
; AVX-NEXT: br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], [[LOOP0:!llvm.loop !.*]]
; AVX: middle.block:
; AVX-NEXT: [[TMP8:%.*]] = call fast double @llvm.vector.reduce.fadd.v4f64(double -0.000000e+00, <4 x double> [[PREDPHI]])
; AVX-NEXT: [[CMP_N:%.*]] = icmp eq i32 32, 32
; AVX-NEXT: br i1 [[CMP_N]], label [[DONE:%.*]], label [[SCALAR_PH]]
; AVX: scalar.ph:
; AVX-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ 32, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
; AVX-NEXT: [[BC_MERGE_RDX:%.*]] = phi double [ 0.000000e+00, [[ENTRY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
; AVX-NEXT: br label [[LOOP:%.*]]
; AVX: loop:
; AVX-NEXT: [[I:%.*]] = phi i32 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[I_NEXT:%.*]], [[NEXT_ITER:%.*]] ]
; AVX-NEXT: [[TOT:%.*]] = phi double [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[TOT_NEXT:%.*]], [[NEXT_ITER]] ]
; AVX-NEXT: [[ADDR:%.*]] = getelementptr double, double* [[ARR]], i32 [[I]]
; AVX-NEXT: [[NEXTVAL:%.*]] = load double, double* [[ADDR]], align 8
; AVX-NEXT: [[TST:%.*]] = fcmp fast une double [[NEXTVAL]], 4.200000e+01
; AVX-NEXT: br i1 [[TST]], label [[DO_ADD:%.*]], label [[NO_ADD:%.*]]
; AVX: do.add:
; AVX-NEXT: [[TOT_NEW:%.*]] = fadd fast double [[TOT]], [[NEXTVAL]]
; AVX-NEXT: br label [[NEXT_ITER]]
; AVX: no.add:
; AVX-NEXT: br label [[NEXT_ITER]]
; AVX: next.iter:
; AVX-NEXT: [[TOT_NEXT]] = phi double [ [[TOT]], [[NO_ADD]] ], [ [[TOT_NEW]], [[DO_ADD]] ]
; AVX-NEXT: [[I_NEXT]] = add i32 [[I]], 1
; AVX-NEXT: [[AGAIN:%.*]] = icmp ult i32 [[I_NEXT]], 32
; AVX-NEXT: br i1 [[AGAIN]], label [[LOOP]], label [[DONE]], [[LOOP2:!llvm.loop !.*]]
; AVX: done:
; AVX-NEXT: [[TOT_NEXT_LCSSA:%.*]] = phi double [ [[TOT_NEXT]], [[NEXT_ITER]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
; AVX-NEXT: ret double [[TOT_NEXT_LCSSA]]
;
entry:
br label %loop
loop:
%i = phi i32 [0, %entry], [%i.next, %next.iter]
%tot = phi double [0.0, %entry], [%tot.next, %next.iter]
%addr = getelementptr double, double* %arr, i32 %i
%nextval = load double, double* %addr
%tst = fcmp fast une double %nextval, 42.0
br i1 %tst, label %do.add, label %no.add
do.add:
%tot.new = fadd fast double %tot, %nextval
br label %next.iter
no.add:
br label %next.iter
next.iter:
%tot.next = phi double [%tot, %no.add], [%tot.new, %do.add]
%i.next = add i32 %i, 1
%again = icmp ult i32 %i.next, 32
br i1 %again, label %loop, label %done
done:
ret double %tot.next
}
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