Pull in r217410 from upstream llvm trunk (by Bob Wilson):

  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!

This should fix clang -O0 on i386 assigning garbage to floats, in
certain scenarios.

Introduced here: http://svnweb.freebsd.org/changeset/base/271597

Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp	(revision 208032)
+++ lib/Target/X86/X86ISelLowering.cpp	(working copy)
@@ -300,6 +300,8 @@ 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);
@@ -1011,8 +1013,6 @@ 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);
Index: test/CodeGen/X86/dont-trunc-store-double-to-float.ll
===================================================================
--- test/CodeGen/X86/dont-trunc-store-double-to-float.ll	(revision 0)
+++ test/CodeGen/X86/dont-trunc-store-double-to-float.ll	(working copy)
@@ -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
+}