From 04934b0feca39e7d7818aa8d9b312c53e78f9785 Mon Sep 17 00:00:00 2001 From: "Duncan P. N. Exon Smith" Date: Thu, 10 Jul 2014 17:13:27 +0000 Subject: [PATCH] InstCombine: Fix a crash in Descale for multiply-by-zero 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 llvm-svn: 212742 --- .../Transforms/InstCombine/InstructionCombining.cpp | 6 ++++++ llvm/test/Transforms/InstCombine/descale-zero.ll | 21 +++++++++++++++++++++ 2 files changed, 27 insertions(+) create mode 100644 llvm/test/Transforms/InstCombine/descale-zero.ll diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp index 46e3bfc..08e2446 100644 --- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -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 diff --git a/llvm/test/Transforms/InstCombine/descale-zero.ll b/llvm/test/Transforms/InstCombine/descale-zero.ll new file mode 100644 index 0000000..7990fdb --- /dev/null +++ b/llvm/test/Transforms/InstCombine/descale-zero.ll @@ -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 +} -- 2.7.4