[Split GEP] handle trunc() in separate-const-offset-from-gep pass.

Let separate-const-offset-from-gep pass handle trunc() when it calculates
constant offset relative to base. The pass itself may insert trunc()
instructions when it canonicalises array indices to pointer-size integers
and needs to handle trunc() in order to evaluate the offset.

Differential Revision: https://reviews.llvm.org/D46732

llvm-svn: 332142

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp b/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
index e8a8328d24c..534fdfdb5e3 100644
--- a/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
+++ b/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
@@ -587,6 +587,10 @@ APInt ConstantOffsetExtractor::find(Value *V, bool SignExtended,
     // Trace into subexpressions for more hoisting opportunities.
     if (CanTraceInto(SignExtended, ZeroExtended, BO, NonNegative))
       ConstantOffset = findInEitherOperand(BO, SignExtended, ZeroExtended);
+  } else if (isa<TruncInst>(V)) {
+    ConstantOffset =
+        find(U->getOperand(0), SignExtended, ZeroExtended, NonNegative)
+            .trunc(BitWidth);
   } else if (isa<SExtInst>(V)) {
     ConstantOffset = find(U->getOperand(0), /* SignExtended */ true,
                           ZeroExtended, NonNegative).sext(BitWidth);
@@ -651,8 +655,9 @@ ConstantOffsetExtractor::distributeExtsAndCloneChain(unsigned ChainIndex) {
   }
 
   if (CastInst *Cast = dyn_cast<CastInst>(U)) {
-    assert((isa<SExtInst>(Cast) || isa<ZExtInst>(Cast)) &&
-           "We only traced into two types of CastInst: sext and zext");
+    assert(
+        (isa<SExtInst>(Cast) || isa<ZExtInst>(Cast) || isa<TruncInst>(Cast)) &&
+        "Only following instructions can be traced: sext, zext & trunc");
     ExtInsts.push_back(Cast);
     UserChain[ChainIndex] = nullptr;
     return distributeExtsAndCloneChain(ChainIndex - 1);