[X86] Use single add/sub for large stack offsets
For large stack offsets the compiler generates multiple immediate mode
sub/add instructions in the prologue/epilogue. This patch makes the
compiler place the final amount to be added/subtracted into a register,
which is then added/substracted with a single operation.
Differential Revision: http://reviews.llvm.org/D7226
llvm-svn: 227458
diff --git a/llvm/test/CodeGen/X86/huge-stack-offset.ll b/llvm/test/CodeGen/X86/huge-stack-offset.ll
new file mode 100644
index 0000000..6195161
--- /dev/null
+++ b/llvm/test/CodeGen/X86/huge-stack-offset.ll
@@ -0,0 +1,59 @@
+; RUN: llc < %s -mtriple=x86_64-linux-unknown | FileCheck %s --check-prefix=CHECK-64
+; RUN: llc < %s -mtriple=i386-linux-unknown | FileCheck %s --check-prefix=CHECK-32
+
+; Test that a large stack offset uses a single add/sub instruction to
+; adjust the stack pointer.
+
+define void @foo() nounwind {
+; CHECK-64-LABEL: foo:
+; CHECK-64: movabsq $50000000{{..}}, %rax
+; CHECK-64-NEXT: subq %rax, %rsp
+; CHECK-64-NOT: subq $2147483647, %rsp
+; CHECK-64: movabsq $50000000{{..}}, [[RAX:%r..]]
+; CHECK-64-NEXT: addq [[RAX]], %rsp
+
+; CHECK-32-LABEL: foo:
+; CHECK-32: movl $50000000{{..}}, %eax
+; CHECK-32-NEXT: subl %eax, %esp
+; CHECK-32-NOT: subl $2147483647, %esp
+; CHECK-32: movl $50000000{{..}}, [[EAX:%e..]]
+; CHECK-32-NEXT: addl [[EAX]], %esp
+ %1 = alloca [5000000000 x i8], align 16
+ %2 = getelementptr inbounds [5000000000 x i8]* %1, i32 0, i32 0
+ call void @bar(i8* %2)
+ ret void
+}
+
+; Verify that we do not clobber the return value.
+
+define i32 @foo2() nounwind {
+; CHECK-64-LABEL: foo2:
+; CHECK-64: movl $10, %eax
+; CHECK-64-NOT: movabsq ${{.*}}, %rax
+
+; CHECK-32-LABEL: foo2:
+; CHECK-32: movl $10, %eax
+; CHECK-32-NOT: movl ${{.*}}, %eax
+ %1 = alloca [5000000000 x i8], align 16
+ %2 = getelementptr inbounds [5000000000 x i8]* %1, i32 0, i32 0
+ call void @bar(i8* %2)
+ ret i32 10
+}
+
+; Verify that we do not clobber EAX when using inreg attribute
+
+define i32 @foo3(i32 inreg %x) nounwind {
+; CHECK-64-LABEL: foo3:
+; CHECK-64: movabsq $50000000{{..}}, %rax
+; CHECK-64-NEXT: subq %rax, %rsp
+
+; CHECK-32-LABEL: foo3:
+; CHECK-32: subl $2147483647, %esp
+; CHECK-32-NOT: movl ${{.*}}, %eax
+ %1 = alloca [5000000000 x i8], align 16
+ %2 = getelementptr inbounds [5000000000 x i8]* %1, i32 0, i32 0
+ call void @bar(i8* %2)
+ ret i32 %x
+}
+
+declare void @bar(i8*)