[llvm] 784937b - [BasicAA] Use smul_ov helper (NFCI)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-11-07T18:14:48+01:00
New Revision: 784937b9bbc56ac039ff8d51c47e1ca6743d9297

URL: https://github.com/llvm/llvm-project/commit/784937b9bbc56ac039ff8d51c47e1ca6743d9297
DIFF: https://github.com/llvm/llvm-project/commit/784937b9bbc56ac039ff8d51c47e1ca6743d9297.diff

LOG: [BasicAA] Use smul_ov helper (NFCI)

Instead of performing the multiplication in double the bit width
and using active bits to determine overflow, use the existing
smul_ov() APInt method to detect overflow.

The smul_ov() implementation is not particularly efficient, but
it's still better than doing this a wide, usually 128-bit, type.

Added: 
    

Modified: 
    llvm/lib/Analysis/BasicAliasAnalysis.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 5de34c57f9a7..8960044e9e31 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -549,9 +549,10 @@ bool BasicAAResult::DecomposeGEPExpression(const Value *V,
       // FIXME: C1*Scale and the other operations in the decomposed
       // (C1*Scale)*V+C2*Scale can also overflow. We should check for this
       // possibility.
-      APInt WideScaledOffset = IndexOffset.sextOrTrunc(MaxPointerSize*2) *
-                                 Scale.sext(MaxPointerSize*2);
-      if (WideScaledOffset.getMinSignedBits() > MaxPointerSize) {
+      bool Overflow;
+      APInt ScaledOffset = IndexOffset.sextOrTrunc(MaxPointerSize)
+                           .smul_ov(Scale, Overflow);
+      if (Overflow) {
         Index = OrigIndex;
         IndexScale = 1;
         IndexOffset = 0;
@@ -560,7 +561,7 @@ bool BasicAAResult::DecomposeGEPExpression(const Value *V,
         if (PointerSize > Width)
           SExtBits += PointerSize - Width;
       } else {
-        Decomposed.OtherOffset += IndexOffset.sextOrTrunc(MaxPointerSize) * Scale;
+        Decomposed.OtherOffset += ScaledOffset;
         Scale *= IndexScale.sextOrTrunc(MaxPointerSize);
       }