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InstCombine: Fix a crash in Descale for multiply-by-zero

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Fix a crash in `InstCombiner::Descale()` when a multiply-by-zero gets
created as an argument to a GEP partway through an iteration, causing
-instcombine to optimize the GEP before the multiply.

rdar://problem/17615671

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212742 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2014-07-10 17:13:27 +00:00
parent c1a6d65d21
commit 5b8419d32e
2 changed files with 27 additions and 0 deletions
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6
lib/Transforms/InstCombine/InstructionCombining.cpp
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@ -1120,6 +1120,12 @@ Value *InstCombiner::Descale(Value *Val, APInt Scale, bool &NoSignedWrap) {
return nullptr;
}
// If Op is zero then Val = Op * Scale.
if (match(Op, m_Zero())) {
NoSignedWrap = true;
return Op;
}
// We know that we can successfully descale, so from here on we can safely
// modify the IR. Op holds the descaled version of the deepest term in the
// expression. NoSignedWrap is 'true' if multiplying Op by Scale is known

21
test/Transforms/InstCombine/descale-zero.ll Normal file
View File

@ -0,0 +1,21 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
define internal i8* @descale_zero() {
entry:
; CHECK: load i16** inttoptr (i64 48 to i16**), align 16
; CHECK-NEXT: bitcast i16*
; CHECK-NEXT: ret i8*
%i16_ptr = load i16** inttoptr (i64 48 to i16**), align 16
%num = load i64* inttoptr (i64 64 to i64*), align 64
%num_times_2 = shl i64 %num, 1
%num_times_2_plus_4 = add i64 %num_times_2, 4
%i8_ptr = bitcast i16* %i16_ptr to i8*
%i8_ptr_num_times_2_plus_4 = getelementptr i8* %i8_ptr, i64 %num_times_2_plus_4
%num_times_neg2 = mul i64 %num, -2
%num_times_neg2_minus_4 = add i64 %num_times_neg2, -4
%addr = getelementptr i8* %i8_ptr_num_times_2_plus_4, i64 %num_times_neg2_minus_4
ret i8* %addr
}