[llvm-commits] [llvm] r84936 - in /llvm/trunk: lib/Analysis/ConstantFolding.cpp test/Transforms/ConstProp/loads.ll
Chris Lattner
sabre at nondot.org
Thu Oct 22 23:23:49 PDT 2009
Author: lattner
Date: Fri Oct 23 01:23:49 2009
New Revision: 84936
URL: http://llvm.org/viewvc/llvm-project?rev=84936&view=rev
Log:
teach libanalysis to fold int and fp loads from almost arbitrary
non-type-safe constant initializers. This sort of thing happens
quite a bit for 4-byte loads out of string constants, unions,
bitfields, and an interesting endianness check from sqlite, which
is something like this:
const int sqlite3one = 1;
# define SQLITE_BIGENDIAN (*(char *)(&sqlite3one)==0)
# define SQLITE_LITTLEENDIAN (*(char *)(&sqlite3one)==1)
# define SQLITE_UTF16NATIVE (SQLITE_BIGENDIAN?SQLITE_UTF16BE:SQLITE_UTF16LE)
all of these macros now constant fold away.
This implements PR3152 and is based on a patch started by Eli, but heavily
modified and extended.
Added:
llvm/trunk/test/Transforms/ConstProp/loads.ll
Modified:
llvm/trunk/lib/Analysis/ConstantFolding.cpp
Modified: llvm/trunk/lib/Analysis/ConstantFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ConstantFolding.cpp?rev=84936&r1=84935&r2=84936&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ConstantFolding.cpp (original)
+++ llvm/trunk/lib/Analysis/ConstantFolding.cpp Fri Oct 23 01:23:49 2009
@@ -93,6 +93,178 @@
return false;
}
+/// ReadDataFromGlobal - Recursive helper to read bits out of global. C is the
+/// constant being copied out of. ByteOffset is an offset into C. CurPtr is the
+/// pointer to copy results into and BytesLeft is the number of bytes left in
+/// the CurPtr buffer. TD is the target data.
+static bool ReadDataFromGlobal(Constant *C, uint64_t ByteOffset,
+ unsigned char *CurPtr, unsigned BytesLeft,
+ const TargetData &TD) {
+ assert(ByteOffset <= TD.getTypeAllocSize(C->getType()) &&
+ "Out of range access");
+
+ if (isa<ConstantAggregateZero>(C) || isa<UndefValue>(C))
+ return true;
+
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
+ if (CI->getBitWidth() > 64 ||
+ (CI->getBitWidth() & 7) != 0)
+ return false;
+
+ uint64_t Val = CI->getZExtValue();
+ unsigned IntBytes = unsigned(CI->getBitWidth()/8);
+
+ for (unsigned i = 0; i != BytesLeft && ByteOffset != IntBytes; ++i) {
+ CurPtr[i] = (unsigned char)(Val >> ByteOffset * 8);
+ ++ByteOffset;
+ }
+ return true;
+ }
+
+ if (ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
+ if (CFP->getType()->isDoubleTy()) {
+ C = ConstantExpr::getBitCast(C, Type::getInt64Ty(C->getContext()));
+ return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD);
+ }
+ if (CFP->getType()->isFloatTy()){
+ C = ConstantExpr::getBitCast(C, Type::getInt32Ty(C->getContext()));
+ return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD);
+ }
+ }
+
+ if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
+ const StructLayout *SL = TD.getStructLayout(CS->getType());
+ unsigned Index = SL->getElementContainingOffset(ByteOffset);
+ uint64_t CurEltOffset = SL->getElementOffset(Index);
+ ByteOffset -= CurEltOffset;
+
+ while (1) {
+ // If the element access is to the element itself and not to tail padding,
+ // read the bytes from the element.
+ uint64_t EltSize = TD.getTypeAllocSize(CS->getOperand(Index)->getType());
+
+ if (ByteOffset < EltSize &&
+ !ReadDataFromGlobal(CS->getOperand(Index), ByteOffset, CurPtr,
+ BytesLeft, TD))
+ return false;
+
+ ++Index;
+
+ // Check to see if we read from the last struct element, if so we're done.
+ if (Index == CS->getType()->getNumElements())
+ return true;
+
+ // If we read all of the bytes we needed from this element we're done.
+ uint64_t NextEltOffset = SL->getElementOffset(Index);
+
+ if (BytesLeft <= NextEltOffset-CurEltOffset-ByteOffset)
+ return true;
+
+ // Move to the next element of the struct.
+ BytesLeft -= NextEltOffset-CurEltOffset-ByteOffset;
+ ByteOffset = 0;
+ CurEltOffset = NextEltOffset;
+ }
+ // not reached.
+ }
+
+ if (ConstantArray *CA = dyn_cast<ConstantArray>(C)) {
+ uint64_t EltSize = TD.getTypeAllocSize(CA->getType()->getElementType());
+ uint64_t Index = ByteOffset / EltSize;
+ uint64_t Offset = ByteOffset - Index * EltSize;
+ for (; Index != CA->getType()->getNumElements(); ++Index) {
+ if (!ReadDataFromGlobal(CA->getOperand(Index), Offset, CurPtr,
+ BytesLeft, TD))
+ return false;
+ if (EltSize >= BytesLeft)
+ return true;
+
+ Offset = 0;
+ BytesLeft -= EltSize;
+ CurPtr += EltSize;
+ }
+ return true;
+ }
+
+ if (ConstantVector *CV = dyn_cast<ConstantVector>(C)) {
+ uint64_t EltSize = TD.getTypeAllocSize(CV->getType()->getElementType());
+ uint64_t Index = ByteOffset / EltSize;
+ uint64_t Offset = ByteOffset - Index * EltSize;
+ for (; Index != CV->getType()->getNumElements(); ++Index) {
+ if (!ReadDataFromGlobal(CV->getOperand(Index), Offset, CurPtr,
+ BytesLeft, TD))
+ return false;
+ if (EltSize >= BytesLeft)
+ return true;
+
+ Offset = 0;
+ BytesLeft -= EltSize;
+ CurPtr += EltSize;
+ }
+ return true;
+ }
+
+ // Otherwise, unknown initializer type.
+ return false;
+}
+
+static Constant *FoldReinterpretLoadFromConstPtr(Constant *C,
+ const TargetData &TD) {
+ const Type *InitializerTy = cast<PointerType>(C->getType())->getElementType();
+ const IntegerType *IntType = dyn_cast<IntegerType>(InitializerTy);
+
+ // If this isn't an integer load we can't fold it directly.
+ if (!IntType) {
+ // If this is a float/double load, we can try folding it as an int32/64 load
+ // and then bitcast the result. This can be useful for union cases.
+ const Type *MapTy;
+ if (InitializerTy->isFloatTy())
+ MapTy = Type::getInt32PtrTy(C->getContext());
+ else if (InitializerTy->isDoubleTy())
+ MapTy = Type::getInt64PtrTy(C->getContext());
+ else
+ return 0;
+
+ C = ConstantExpr::getBitCast(C, MapTy);
+ if (Constant *Res = FoldReinterpretLoadFromConstPtr(C, TD))
+ return ConstantExpr::getBitCast(Res, InitializerTy);
+ return 0;
+ }
+
+ unsigned BytesLoaded = (IntType->getBitWidth() + 7) / 8;
+ if (BytesLoaded > 8 || BytesLoaded == 0) return 0;
+
+ GlobalValue *GVal;
+ int64_t Offset;
+ if (!IsConstantOffsetFromGlobal(C, GVal, Offset, TD))
+ return 0;
+
+ GlobalVariable *GV = dyn_cast<GlobalVariable>(GVal);
+ if (!GV || !GV->isConstant() || !GV->hasInitializer() ||
+ !GV->hasDefinitiveInitializer() ||
+ !GV->getInitializer()->getType()->isSized())
+ return 0;
+
+ // If we're loading off the beginning of the global, some bytes may be valid,
+ // but we don't try to handle this.
+ if (Offset < 0) return 0;
+
+ // If we're not accessing anything in this constant, the result is undefined.
+ if (uint64_t(Offset) >= TD.getTypeAllocSize(GV->getInitializer()->getType()))
+ return UndefValue::get(IntType);
+
+ unsigned char RawBytes[8] = {0};
+ if (!ReadDataFromGlobal(GV->getInitializer(), Offset, RawBytes,
+ BytesLoaded, TD))
+ return 0;
+
+ uint64_t ResultVal = 0;
+ for (unsigned i = 0; i != BytesLoaded; ++i)
+ ResultVal |= (uint64_t)RawBytes[i] << (i * 8);
+
+ return ConstantInt::get(IntType, ResultVal);
+}
+
/// ConstantFoldLoadFromConstPtr - Return the value that a load from C would
/// produce if it is constant and determinable. If this is not determinable,
/// return null.
@@ -119,20 +291,20 @@
// directly if string length is small enough.
std::string Str;
if (TD && GetConstantStringInfo(CE->getOperand(0), Str) && !Str.empty()) {
- unsigned len = Str.length();
+ unsigned StrLen = Str.length();
const Type *Ty = cast<PointerType>(CE->getType())->getElementType();
- unsigned numBits = Ty->getPrimitiveSizeInBits();
+ unsigned NumBits = Ty->getPrimitiveSizeInBits();
// Replace LI with immediate integer store.
- if ((numBits >> 3) == len + 1) {
- APInt StrVal(numBits, 0);
- APInt SingleChar(numBits, 0);
+ if ((NumBits >> 3) == StrLen + 1) {
+ APInt StrVal(NumBits, 0);
+ APInt SingleChar(NumBits, 0);
if (TD->isLittleEndian()) {
- for (signed i = len-1; i >= 0; i--) {
+ for (signed i = StrLen-1; i >= 0; i--) {
SingleChar = (uint64_t) Str[i] & UCHAR_MAX;
StrVal = (StrVal << 8) | SingleChar;
}
} else {
- for (unsigned i = 0; i < len; i++) {
+ for (unsigned i = 0; i < StrLen; i++) {
SingleChar = (uint64_t) Str[i] & UCHAR_MAX;
StrVal = (StrVal << 8) | SingleChar;
}
@@ -156,6 +328,11 @@
}
}
+ // Try hard to fold loads from bitcasted strange and non-type-safe things. We
+ // currently don't do any of this for big endian systems. It can be
+ // generalized in the future if someone is interested.
+ if (TD && TD->isLittleEndian())
+ return FoldReinterpretLoadFromConstPtr(CE, *TD);
return 0;
}
@@ -164,7 +341,7 @@
if (Constant *C = dyn_cast<Constant>(LI->getOperand(0)))
return ConstantFoldLoadFromConstPtr(C, TD);
-
+
return 0;
}
Added: llvm/trunk/test/Transforms/ConstProp/loads.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ConstProp/loads.ll?rev=84936&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/ConstProp/loads.ll (added)
+++ llvm/trunk/test/Transforms/ConstProp/loads.ll Fri Oct 23 01:23:49 2009
@@ -0,0 +1,68 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
+
+ at test1 = constant {{i32,i8},i32} {{i32,i8} { i32 -559038737, i8 186 }, i32 -889275714 }
+ at test2 = constant double 1.0
+
+; Simple load
+define i32 @test1() {
+ %r = load i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0)
+ ret i32 %r
+; @test1
+; CHECK: ret i32 -559038737
+}
+
+; PR3152
+; Load of first 16 bits of 32-bit value.
+define i16 @test2() {
+ %r = load i16* bitcast(i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0) to i16*)
+ ret i16 %r
+
+; @test2
+; CHECK: ret i16 -16657
+}
+
+; Load of second 16 bits of 32-bit value.
+define i16 @test3() {
+ %r = load i16* getelementptr(i16* bitcast(i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0) to i16*), i32 1)
+ ret i16 %r
+
+; @test3
+; CHECK: ret i16 -8531
+}
+
+; Load of 8 bit field + tail padding.
+define i16 @test4() {
+ %r = load i16* getelementptr(i16* bitcast(i32* getelementptr ({{i32,i8},i32}* @test1, i32 0, i32 0, i32 0) to i16*), i32 2)
+ ret i16 %r
+; @test4
+; CHECK: ret i16 186
+}
+
+; Load of double bits.
+define i64 @test6() {
+ %r = load i64* bitcast(double* @test2 to i64*)
+ ret i64 %r
+
+; @test6
+; CHECK: ret i64 4607182418800017408
+}
+
+; Load of double bits.
+define i16 @test7() {
+ %r = load i16* bitcast(double* @test2 to i16*)
+ ret i16 %r
+
+; @test7
+; CHECK: ret i16 0
+}
+
+; Double load.
+define double @test8() {
+ %r = load double* bitcast({{i32,i8},i32}* @test1 to double*)
+ ret double %r
+
+; @test8
+; CHECK: ret double 0xDEADBEBA
+}
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