[X86] Add test for interaction between pushf/popf and redzones

As requested on D92695

Author: rnk

llvm/test/CodeGen/X86/red-zone.ll

@@ -1,11 +1,13 @@
 ; RUN: llc < %s -mcpu=generic -mtriple=x86_64-linux | FileCheck %s
 
+@flags_gv = global i64 0
+
 ; First without noredzone.
 ; CHECK-LABEL: f0:
 ; CHECK: -4(%rsp)
 ; CHECK: -4(%rsp)
 ; CHECK: ret
-define x86_fp80 @f0(float %f) nounwind readnone {
+define x86_fp80 @f0(float %f) nounwind {
 entry:
 	%0 = fpext float %f to x86_fp80		; <x86_fp80> [#uses=1]
 	ret x86_fp80 %0
@@ -18,8 +20,42 @@ entry:
 ; CHECK: (%rsp)
 ; CHECK: addq $4, %rsp
 ; CHECK: ret
-define x86_fp80 @f1(float %f) nounwind readnone noredzone {
+define x86_fp80 @f1(float %f) nounwind noredzone {
 entry:
 	%0 = fpext float %f to x86_fp80		; <x86_fp80> [#uses=1]
 	ret x86_fp80 %0
 }
+
+declare i64 @llvm.x86.flags.read.u64()
+declare void @llvm.x86.flags.write.u64(i64)
+
+
+; pushfq and popfq prevent redzones.
+; CHECK-LABEL: norz_flags_read:
+; CHECK: subq ${{[0-9]+}}, %rsp
+; CHECK: pushfq
+; CHECK: popq
+; CHECK: (%rsp)
+; CHECK: (%rsp)
+; CHECK: ret
+define x86_fp80 @norz_flags_read(float %f) nounwind {
+entry:
+  %flags = call i64 @llvm.x86.flags.read.u64()
+  store i64 %flags, i64* @flags_gv
+  %0 = fpext float %f to x86_fp80
+  ret x86_fp80 %0
+}
+
+; CHECK-LABEL: norz_flags_write:
+; CHECK: subq ${{[0-9]+}}, %rsp
+; CHECK: pushq
+; CHECK: popfq
+; CHECK: (%rsp)
+; CHECK: (%rsp)
+; CHECK: ret
+define x86_fp80 @norz_flags_write(float %f, i64 %flags) nounwind {
+entry:
+  call void @llvm.x86.flags.write.u64(i64 %flags)
+  %0 = fpext float %f to x86_fp80
+  ret x86_fp80 %0
+}