Set trunc store action to Expand for all X86 targets.

When compiling without SSE2, isTruncStoreLegal(F64, F32) would return Legal, whereas with SSE2 it would return Expand. And since the Target doesn't seem to actually handle a truncstore for double -> float, it would just output a store of a full double in the space for a float hence overwriting other bits on the stack.

Patch by Luqman Aden!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217410 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86ISelLowering.cpp

@@ -317,6 +317,8 @@ void X86TargetLowering::resetOperationActions() {
   setTruncStoreAction(MVT::i32, MVT::i8 , Expand);
   setTruncStoreAction(MVT::i16, MVT::i8,  Expand);
 
+  setTruncStoreAction(MVT::f64, MVT::f32, Expand);
+
   // SETOEQ and SETUNE require checking two conditions.
   setCondCodeAction(ISD::SETOEQ, MVT::f32, Expand);
   setCondCodeAction(ISD::SETOEQ, MVT::f64, Expand);
@@ -1057,8 +1059,6 @@ void X86TargetLowering::resetOperationActions() {
       AddPromotedToType (ISD::SELECT, VT, MVT::v2i64);
     }
 
-    setTruncStoreAction(MVT::f64, MVT::f32, Expand);
-
     // Custom lower v2i64 and v2f64 selects.
     setOperationAction(ISD::LOAD,               MVT::v2f64, Legal);
     setOperationAction(ISD::LOAD,               MVT::v2i64, Legal);

test/CodeGen/X86/dont-trunc-store-double-to-float.ll

@@ -0,0 +1,20 @@
+; RUN: llc -march=x86 < %s | FileCheck %s
+
+; CHECK-LABEL: @bar
+; CHECK: movl $1074339512,
+; CHECK: movl $1374389535,
+; CHECK: movl $1078523331,
+define void @bar() unnamed_addr {
+entry-block:
+  %a = alloca double
+  %b = alloca float
+
+  store double 3.140000e+00, double* %a
+  %0 = load double* %a
+
+  %1 = fptrunc double %0 to float
+
+  store float %1, float* %b
+
+  ret void
+}