From 7e621e9d5e011a50b4e0917ef0b6367c44567a90 Mon Sep 17 00:00:00 2001 From: Owen Anderson Date: Sun, 8 Mar 2015 21:53:59 +0000 Subject: [PATCH] Teach DataLayout to infer a plausible alignment for things even when nothing is specified by the user. llvm-svn: 231613 --- llvm/lib/IR/DataLayout.cpp | 17 ++++++++++++++--- llvm/test/Transforms/InstCombine/default-alignment.ll | 10 ++++++++++ 2 files changed, 24 insertions(+), 3 deletions(-) create mode 100644 llvm/test/Transforms/InstCombine/default-alignment.ll diff --git a/llvm/lib/IR/DataLayout.cpp b/llvm/lib/IR/DataLayout.cpp index c70d7c6..5dcb5fb 100644 --- a/llvm/lib/IR/DataLayout.cpp +++ b/llvm/lib/IR/DataLayout.cpp @@ -479,9 +479,7 @@ unsigned DataLayout::getAlignmentInfo(AlignTypeEnum AlignType, // If we didn't find an integer alignment, fall back on most conservative. if (AlignType == INTEGER_ALIGN) { BestMatchIdx = LargestInt; - } else { - assert(AlignType == VECTOR_ALIGN && "Unknown alignment type!"); - + } else if (AlignType == VECTOR_ALIGN) { // By default, use natural alignment for vector types. This is consistent // with what clang and llvm-gcc do. unsigned Align = getTypeAllocSize(cast(Ty)->getElementType()); @@ -494,6 +492,19 @@ unsigned DataLayout::getAlignmentInfo(AlignTypeEnum AlignType, } } + // If we still couldn't find a reasonable default alignment, fall back + // to a simple heuristic that the alignment is the first power of two + // greater-or-equal to the store size of the type. This is a reasonable + // approximation of reality, and if the user wanted something less + // less conservative, they should have specified it explicitly in the data + // layout. + if (BestMatchIdx == -1) { + unsigned Align = getTypeStoreSize(Ty); + if (Align & (Align-1)) + Align = NextPowerOf2(Align); + return Align; + } + // Since we got a "best match" index, just return it. return ABIInfo ? Alignments[BestMatchIdx].ABIAlign : Alignments[BestMatchIdx].PrefAlign; diff --git a/llvm/test/Transforms/InstCombine/default-alignment.ll b/llvm/test/Transforms/InstCombine/default-alignment.ll new file mode 100644 index 0000000..718da21 --- /dev/null +++ b/llvm/test/Transforms/InstCombine/default-alignment.ll @@ -0,0 +1,10 @@ +; RUN: opt -verify -instcombine < %s +%Foo = type <{ i8, x86_fp80 }> + +define i8 @t(%Foo* %arg) { +entry: + %0 = getelementptr %Foo, %Foo* %arg, i32 0, i32 0 + %1 = load i8, i8* %0, align 1 + ret i8 %1 +} + -- 2.7.4