[BasicAA] NFC - utility function for two's complement wrap-around
llvm-svn: 259290
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index b373792..b11cb51 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -37,16 +37,17 @@
#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
+
+#define DEBUG_TYPE "basicaa"
+
using namespace llvm;
/// Enable analysis of recursive PHI nodes.
static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden,
cl::init(false));
-
/// SearchLimitReached / SearchTimes shows how often the limit of
/// to decompose GEPs is reached. It will affect the precision
/// of basic alias analysis.
-#define DEBUG_TYPE "basicaa"
STATISTIC(SearchLimitReached, "Number of times the limit to "
"decompose GEPs is reached");
STATISTIC(SearchTimes, "Number of times a GEP is decomposed");
@@ -319,6 +320,16 @@
return V;
}
+/// To ensure a pointer offset fits in an integer of size PointerSize
+/// (in bits) when that size is smaller than 64. This is an issue in
+/// particular for 32b programs with negative indices that rely on two's
+/// complement wrap-arounds for correct alias information.
+static int64_t adjustToPointerSize(int64_t Offset, unsigned PointerSize) {
+ assert(PointerSize <= 64 && "Invalid PointerSize!");
+ unsigned ShiftBits = 64 - PointerSize;
+ return (uint64_t)Offset << ShiftBits >> ShiftBits;
+}
+
/// If V is a symbolic pointer expression, decompose it into a base pointer
/// with a constant offset and a number of scaled symbolic offsets.
///
@@ -387,6 +398,7 @@
unsigned AS = GEPOp->getPointerAddressSpace();
// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
gep_type_iterator GTI = gep_type_begin(GEPOp);
+ unsigned PointerSize = DL.getPointerSizeInBits(AS);
for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end();
I != E; ++I) {
const Value *Index = *I;
@@ -415,7 +427,6 @@
// If the integer type is smaller than the pointer size, it is implicitly
// sign extended to pointer size.
unsigned Width = Index->getType()->getIntegerBitWidth();
- unsigned PointerSize = DL.getPointerSizeInBits(AS);
if (PointerSize > Width)
SExtBits += PointerSize - Width;
@@ -445,10 +456,7 @@
// Make sure that we have a scale that makes sense for this target's
// pointer size.
- if (unsigned ShiftBits = 64 - PointerSize) {
- Scale <<= ShiftBits;
- Scale = (int64_t)Scale >> ShiftBits;
- }
+ Scale = adjustToPointerSize(Scale, PointerSize);
if (Scale) {
VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,