Avoid storing and reloading zeros and other constants from stack slots

by flagging the associated instructions as being trivially rematerializable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@41775 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/zero-remat.ll

@@ -0,0 +1,14 @@
+; RUN: llvm-as < %s | llc -march=x86-64 | grep xor | count 4
+; RUN: llvm-as < %s | llc -march=x86-64 -stats -info-output-file - | grep asm-printer | grep 12
+
+declare void @bar(double %x)
+declare void @barf(float %x)
+
+define double @foo() {
+  call void @bar(double 0.0)
+  ret double 0.0
+}
+define float @foof() {
+  call void @barf(float 0.0)
+  ret float 0.0
+}