[SCCP] Fold constants as we build them whne visiting cast instructions.

This should be slightly more efficient and could avoid spurious overdefined
markings, as Eli pointed out.

Differential Revision:  http://reviews.llvm.org/D22122

llvm-svn: 274905

2 files changed, 13 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index d4c156e994c..adc70d917f5 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -760,8 +760,10 @@ void SCCPSolver::visitCastInst(CastInst &I) {
   if (OpSt.isOverdefined())          // Inherit overdefinedness of operand
     markOverdefined(&I);
   else if (OpSt.isConstant()) {
-    Constant *C =
-        ConstantExpr::getCast(I.getOpcode(), OpSt.getConstant(), I.getType());
+    // Fold the constant as we build.
+    Constant *C = ConstantFoldCastOperand(
+        I.getOpcode(), getValueState(I.getOperand(0)).getConstant(),
+        I.getType(), DL);
     if (isa<UndefValue>(C))
       return;
     // Propagate constant value
diff --git a/llvm/test/Transforms/SCCP/bitcast.ll b/llvm/test/Transforms/SCCP/bitcast.ll
new file mode 100644
index 00000000000..285823512e5
--- /dev/null
+++ b/llvm/test/Transforms/SCCP/bitcast.ll
@@ -0,0 +1,9 @@
+; RUN: opt < %s -ipsccp -S | FileCheck %s
+
+define i128 @vector_to_int_cast() {
+  %A = bitcast <4 x i32> <i32 1073741824, i32 1073741824, i32 1073741824, i32 1073741824> to i128
+  ret i128 %A
+}
+
+; CHECK: define i128 @vector_to_int_cast(
+; CHECK-NEXT:  ret i128 85070591750041656499021422275829170176