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14476b73f7
The original patch of the A->B->A BitCast optimization was reverted by r274094 because it may cause infinite loop inside compiler https://llvm.org/bugs/show_bug.cgi?id=27996. The problem is with following code xB = load (type B); xA = load (type A); +yA = (A)xB; B -> A +zAn = PHI[yA, xA]; PHI +zBn = (B)zAn; // A -> B store zAn; store zBn; optimizeBitCastFromPhi generates +zBn = (B)zAn; // A -> B and expects it will be combined with the following store instruction to another store zAn Unfortunately before combineStoreToValueType is called on the store instruction, optimizeBitCastFromPhi is called on the new BitCast again, and this pattern repeats indefinitely. optimizeBitCastFromPhi only generates BitCast for load/store instructions, only the BitCast before store can cause the reexecution of optimizeBitCastFromPhi, and BitCast before store can easily be handled by InstCombineLoadStoreAlloca.cpp. So the solution to the problem is if all users of a CI are store instructions, we should not do optimizeBitCastFromPhi on it. Then optimizeBitCastFromPhi will not be called on the new BitCast instructions. Differential Revision: https://reviews.llvm.org/D23896 llvm-svn: 285116
42 lines
950 B
LLVM
42 lines
950 B
LLVM
; RUN: opt < %s -instcombine -S | FileCheck %s
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@i = constant i32 1, align 4
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@f = constant float 0x3FF19999A0000000, align 4
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@cmp = common global i32 0, align 4
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@resf = common global float* null, align 8
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@resi = common global i32* null, align 8
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define i32 @foo() {
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entry:
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br label %while.cond
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while.cond:
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%res.0 = phi i32* [ null, %entry ], [ @i, %if.then ], [ bitcast (float* @f to i32*), %if.else ]
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%0 = load i32, i32* @cmp, align 4
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%shr = ashr i32 %0, 1
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store i32 %shr, i32* @cmp, align 4
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%tobool = icmp ne i32 %shr, 0
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br i1 %tobool, label %while.body, label %while.end
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while.body:
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%and = and i32 %shr, 1
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%tobool1 = icmp ne i32 %and, 0
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br i1 %tobool1, label %if.then, label %if.else
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if.then:
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br label %while.cond
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if.else:
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br label %while.cond
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while.end:
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%1 = bitcast i32* %res.0 to float*
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store float* %1, float** @resf, align 8
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store i32* %res.0, i32** @resi, align 8
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ret i32 0
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; CHECK-NOT: bitcast i32
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}
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