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clang-p2996/llvm/test/Transforms/CodeGenPrepare/X86/select.ll
Juneyoung Lee 6ad63606ea [CodeGenPrepare] Freeze condition when transforming select to br 
Summary:
This is a simple fix for CodeGenPrepare that freezes branch condition when transforming select to branch.
If it is not frozen, instsimplify or the later pipeline can potentially exploit undefined behavior.

The diff shows optimized form becase D75859 and D76048 already made a few changes to CodeGenPrepare for optimizing freeze(cmp).

Reviewers: jdoerfert, spatel, lebedev.ri, efriedma

Reviewed By: lebedev.ri

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76179
2020-03-16 12:46:20 +09:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -codegenprepare -S < %s | FileCheck %s
; RUN: opt -debugify -codegenprepare -S < %s | FileCheck %s -check-prefix=DEBUG
target triple = "x86_64-unknown-unknown"
; Nothing to sink and convert here.
define i32 @no_sink(double %a, double* %b, i32 %x, i32 %y) {
; CHECK-LABEL: @no_sink(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[LOAD:%.*]] = load double, double* [[B:%.*]], align 8
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt double [[LOAD]], [[A:%.*]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[X:%.*]], i32 [[Y:%.*]]
; CHECK-NEXT: ret i32 [[SEL]]
;
entry:
%load = load double, double* %b, align 8
%cmp = fcmp olt double %load, %a
%sel = select i1 %cmp, i32 %x, i32 %y
ret i32 %sel
}
; An 'fdiv' is expensive, so sink it rather than speculatively execute it.
define float @fdiv_true_sink(float %a, float %b) {
; CHECK-LABEL: @fdiv_true_sink(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 1.000000e+00
; CHECK-NEXT: br i1 [[CMP]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_END:%.*]]
; CHECK: select.true.sink:
; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[A]], [[B:%.*]]
; CHECK-NEXT: br label [[SELECT_END]]
; CHECK: select.end:
; CHECK-NEXT: [[SEL:%.*]] = phi float [ [[DIV]], [[SELECT_TRUE_SINK]] ], [ 2.000000e+00, [[ENTRY:%.*]] ]
; CHECK-NEXT: ret float [[SEL]]
;
; DEBUG-LABEL: @fdiv_true_sink(
; DEBUG-NEXT: entry:
; DEBUG-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
; DEBUG-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 1.000000e+00, !dbg !24
; DEBUG-NEXT: call void @llvm.dbg.value(metadata i1 [[CMP]]
; DEBUG-NEXT: br i1 [[CMP]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_END:%.*]], !dbg
; DEBUG: select.true.sink:
; DEBUG-NEXT: [[DIV:%.*]] = fdiv float [[A]], [[B:%.*]]
; DEBUG-NEXT: call void @llvm.dbg.value(metadata float [[DIV]]
; DEBUG-NEXT: br label [[SELECT_END]], !dbg
; DEBUG: select.end:
; DEBUG-NEXT: [[SEL:%.*]] = phi float [ [[DIV]], [[SELECT_TRUE_SINK]] ], [ 2.000000e+00, [[ENTRY:%.*]] ], !dbg
; DEBUG-NEXT: call void @llvm.dbg.value(metadata float [[SEL]]
; DEBUG-NEXT: ret float [[SEL]]
;
entry:
%div = fdiv float %a, %b
%cmp = fcmp ogt float %a, 1.0
%sel = select i1 %cmp, float %div, float 2.0
ret float %sel
}
define float @fdiv_false_sink(float %a, float %b) {
; CHECK-LABEL: @fdiv_false_sink(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 3.000000e+00
; CHECK-NEXT: br i1 [[CMP]], label [[SELECT_END:%.*]], label [[SELECT_FALSE_SINK:%.*]]
; CHECK: select.false.sink:
; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[A]], [[B:%.*]]
; CHECK-NEXT: br label [[SELECT_END]]
; CHECK: select.end:
; CHECK-NEXT: [[SEL:%.*]] = phi float [ 4.000000e+00, [[ENTRY:%.*]] ], [ [[DIV]], [[SELECT_FALSE_SINK]] ]
; CHECK-NEXT: ret float [[SEL]]
;
; DEBUG-LABEL: @fdiv_false_sink(
; DEBUG-NEXT: entry:
; DEBUG-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
; DEBUG-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 3.000000e+00, !dbg !33
; DEBUG-NEXT: call void @llvm.dbg.value(metadata i1 [[CMP]]
; DEBUG-NEXT: br i1 [[CMP]], label [[SELECT_END:%.*]], label [[SELECT_FALSE_SINK:%.*]], !dbg
; DEBUG: select.false.sink:
; DEBUG-NEXT: [[DIV:%.*]] = fdiv float [[A]], [[B:%.*]]
; DEBUG-NEXT: call void @llvm.dbg.value(metadata float [[DIV]]
; DEBUG-NEXT: br label [[SELECT_END]], !dbg
; DEBUG: select.end:
; DEBUG-NEXT: [[SEL:%.*]] = phi float [ 4.000000e+00, [[ENTRY:%.*]] ], [ [[DIV]], [[SELECT_FALSE_SINK]] ], !dbg
; DEBUG-NEXT: call void @llvm.dbg.value(metadata float [[SEL]]
; DEBUG-NEXT: ret float [[SEL]], !dbg
;
entry:
%div = fdiv float %a, %b
%cmp = fcmp ogt float %a, 3.0
%sel = select i1 %cmp, float 4.0, float %div
ret float %sel
}
define float @fdiv_both_sink(float %a, float %b) {
; CHECK-LABEL: @fdiv_both_sink(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 5.000000e+00
; CHECK-NEXT: br i1 [[CMP]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_FALSE_SINK:%.*]]
; CHECK: select.true.sink:
; CHECK-NEXT: [[DIV1:%.*]] = fdiv float [[A]], [[B:%.*]]
; CHECK-NEXT: br label [[SELECT_END:%.*]]
; CHECK: select.false.sink:
; CHECK-NEXT: [[DIV2:%.*]] = fdiv float [[B]], [[A]]
; CHECK-NEXT: br label [[SELECT_END]]
; CHECK: select.end:
; CHECK-NEXT: [[SEL:%.*]] = phi float [ [[DIV1]], [[SELECT_TRUE_SINK]] ], [ [[DIV2]], [[SELECT_FALSE_SINK]] ]
; CHECK-NEXT: ret float [[SEL]]
;
entry:
%div1 = fdiv float %a, %b
%div2 = fdiv float %b, %a
%cmp = fcmp ogt float %a, 5.0
%sel = select i1 %cmp, float %div1, float %div2
ret float %sel
}
; But if the select is marked unpredictable, then don't turn it into a branch.
define float @unpredictable_select(float %a, float %b) {
; CHECK-LABEL: @unpredictable_select(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[A]], 1.000000e+00
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], float [[DIV]], float 2.000000e+00, !unpredictable !0
; CHECK-NEXT: ret float [[SEL]]
;
entry:
%div = fdiv float %a, %b
%cmp = fcmp ogt float %a, 1.0
%sel = select i1 %cmp, float %div, float 2.0, !unpredictable !0
ret float %sel
}
!0 = !{}
; An 'fadd' is not too expensive, so it's ok to speculate.
define float @fadd_no_sink(float %a, float %b) {
; CHECK-LABEL: @fadd_no_sink(
; CHECK-NEXT: [[ADD:%.*]] = fadd float [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float 6.000000e+00, [[A]]
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], float [[ADD]], float 7.000000e+00
; CHECK-NEXT: ret float [[SEL]]
;
%add = fadd float %a, %b
%cmp = fcmp ogt float 6.0, %a
%sel = select i1 %cmp, float %add, float 7.0
ret float %sel
}
; Possible enhancement: sinkability is only calculated with the direct
; operand of the select, so we don't try to sink this. The fdiv cost is not
; taken into account.
define float @fdiv_no_sink(float %a, float %b) {
; CHECK-LABEL: @fdiv_no_sink(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[ADD:%.*]] = fadd float [[DIV]], [[B]]
; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[A]], 1.000000e+00
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], float [[ADD]], float 8.000000e+00
; CHECK-NEXT: ret float [[SEL]]
;
entry:
%div = fdiv float %a, %b
%add = fadd float %div, %b
%cmp = fcmp ogt float %a, 1.0
%sel = select i1 %cmp, float %add, float 8.0
ret float %sel
}
; Do not transform the CFG if the select operands may have side effects.
declare i64* @bar(i32, i32, i32)
declare i64* @baz(i32, i32, i32)
define i64* @calls_no_sink(i32 %in) {
; CHECK-LABEL: @calls_no_sink(
; CHECK-NEXT: [[CALL1:%.*]] = call i64* @bar(i32 1, i32 2, i32 3)
; CHECK-NEXT: [[CALL2:%.*]] = call i64* @baz(i32 1, i32 2, i32 3)
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne i32 [[IN:%.*]], 0
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[TOBOOL]], i64* [[CALL1]], i64* [[CALL2]]
; CHECK-NEXT: ret i64* [[SEL]]
;
%call1 = call i64* @bar(i32 1, i32 2, i32 3)
%call2 = call i64* @baz(i32 1, i32 2, i32 3)
%tobool = icmp ne i32 %in, 0
%sel = select i1 %tobool, i64* %call1, i64* %call2
ret i64* %sel
}
define i32 @sdiv_no_sink(i32 %a, i32 %b) {
; CHECK-LABEL: @sdiv_no_sink(
; CHECK-NEXT: [[DIV1:%.*]] = sdiv i32 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[DIV2:%.*]] = sdiv i32 [[B]], [[A]]
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[A]], 5
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[DIV1]], i32 [[DIV2]]
; CHECK-NEXT: ret i32 [[SEL]]
;
%div1 = sdiv i32 %a, %b
%div2 = sdiv i32 %b, %a
%cmp = icmp sgt i32 %a, 5
%sel = select i1 %cmp, i32 %div1, i32 %div2
ret i32 %sel
}
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