Teach the inliner how to preserve musttail invariants

The interesting case is what happens when you inline a musttail call
through a musttail call site.  In this case, we can't break perfect
forwarding or allow any stack growth.

Instead of merging control flow from the inlined return instruction
after a musttail call into the body of the caller, leave the inlined
return instruction in the caller so that the musttail call stays in the
tail position.

More work is required in http://reviews.llvm.org/D3630 to handle the
case where the inlined function has dynamic allocas or byval arguments.

Reviewers: chandlerc

Differential Revision: http://reviews.llvm.org/D3491

llvm-svn: 208910

1 files changed, 140 insertions, 9 deletions

diff --git a/llvm/test/Transforms/Inline/inline-tail.ll b/llvm/test/Transforms/Inline/inline-tail.ll
index 8bb059d01a0..565491adf5b 100644
--- a/llvm/test/Transforms/Inline/inline-tail.ll
+++ b/llvm/test/Transforms/Inline/inline-tail.ll
@@ -1,15 +1,146 @@
-; RUN: opt < %s -inline -S | not grep tail
+; RUN: opt < %s -inline -S | FileCheck %s
 
-declare void @bar(i32*)
+; We have to apply the less restrictive TailCallKind of the call site being
+; inlined and any call sites cloned into the caller.
 
-define internal void @foo(i32* %P) {
-        tail call void @bar( i32* %P )
-        ret void
+; No tail marker after inlining, since test_capture_c captures an alloca.
+; CHECK: define void @test_capture_a(
+; CHECK-NOT: tail
+; CHECK: call void @test_capture_c(
+
+declare void @test_capture_c(i32*)
+define internal void @test_capture_b(i32* %P) {
+  tail call void @test_capture_c(i32* %P)
+  ret void
+}
+define void @test_capture_a() {
+  %A = alloca i32  		; captured by test_capture_b
+  call void @test_capture_b(i32* %A)
+  ret void
+}
+
+; No musttail marker after inlining, since the prototypes don't match.
+; CHECK: define void @test_proto_mismatch_a(
+; CHECK-NOT: musttail
+; CHECK: call void @test_proto_mismatch_c(
+
+declare void @test_proto_mismatch_c(i32*)
+define internal void @test_proto_mismatch_b(i32* %p) {
+  musttail call void @test_proto_mismatch_c(i32* %p)
+  ret void
+}
+define void @test_proto_mismatch_a() {
+  call void @test_proto_mismatch_b(i32* null)
+  ret void
 }
 
-define void @caller() {
-        %A = alloca i32         ; <i32*> [#uses=1]
-        call void @foo( i32* %A )
-        ret void
+; After inlining through a musttail call site, we need to keep musttail markers
+; to prevent unbounded stack growth.
+; CHECK: define void @test_musttail_basic_a(
+; CHECK: musttail call void @test_musttail_basic_c(
+
+declare void @test_musttail_basic_c(i32* %p)
+define internal void @test_musttail_basic_b(i32* %p) {
+  musttail call void @test_musttail_basic_c(i32* %p)
+  ret void
+}
+define void @test_musttail_basic_a(i32* %p) {
+  musttail call void @test_musttail_basic_b(i32* %p)
+  ret void
+}
+
+; We can't merge the returns.
+; CHECK: define void @test_multiret_a(
+; CHECK: musttail call void @test_multiret_c(
+; CHECK-NEXT: ret void
+; CHECK: musttail call void @test_multiret_d(
+; CHECK-NEXT: ret void
+
+declare void @test_multiret_c(i1 zeroext %b)
+declare void @test_multiret_d(i1 zeroext %b)
+define internal void @test_multiret_b(i1 zeroext %b) {
+  br i1 %b, label %c, label %d
+c:
+  musttail call void @test_multiret_c(i1 zeroext %b)
+  ret void
+d:
+  musttail call void @test_multiret_d(i1 zeroext %b)
+  ret void
+}
+define void @test_multiret_a(i1 zeroext %b) {
+  musttail call void @test_multiret_b(i1 zeroext %b)
+  ret void
 }
 
+; We have to avoid bitcast chains.
+; CHECK: define i32* @test_retptr_a(
+; CHECK: musttail call i8* @test_retptr_c(
+; CHECK-NEXT: bitcast i8* {{.*}} to i32*
+; CHECK-NEXT: ret i32*
+
+declare i8* @test_retptr_c()
+define internal i16* @test_retptr_b() {
+  %rv = musttail call i8* @test_retptr_c()
+  %v = bitcast i8* %rv to i16*
+  ret i16* %v
+}
+define i32* @test_retptr_a() {
+  %rv = musttail call i16* @test_retptr_b()
+  %v = bitcast i16* %rv to i32*
+  ret i32* %v
+}
+
+; Combine the last two cases: multiple returns with pointer bitcasts.
+; CHECK: define i32* @test_multiptrret_a(
+; CHECK: musttail call i8* @test_multiptrret_c(
+; CHECK-NEXT: bitcast i8* {{.*}} to i32*
+; CHECK-NEXT: ret i32*
+; CHECK: musttail call i8* @test_multiptrret_d(
+; CHECK-NEXT: bitcast i8* {{.*}} to i32*
+; CHECK-NEXT: ret i32*
+
+declare i8* @test_multiptrret_c(i1 zeroext %b)
+declare i8* @test_multiptrret_d(i1 zeroext %b)
+define internal i16* @test_multiptrret_b(i1 zeroext %b) {
+  br i1 %b, label %c, label %d
+c:
+  %c_rv = musttail call i8* @test_multiptrret_c(i1 zeroext %b)
+  %c_v = bitcast i8* %c_rv to i16*
+  ret i16* %c_v
+d:
+  %d_rv = musttail call i8* @test_multiptrret_d(i1 zeroext %b)
+  %d_v = bitcast i8* %d_rv to i16*
+  ret i16* %d_v
+}
+define i32* @test_multiptrret_a(i1 zeroext %b) {
+  %rv = musttail call i16* @test_multiptrret_b(i1 zeroext %b)
+  %v = bitcast i16* %rv to i32*
+  ret i32* %v
+}
+
+; Inline a musttail call site which contains a normal return and a musttail call.
+; CHECK: define i32 @test_mixedret_a(
+; CHECK: br i1 %b
+; CHECK: musttail call i32 @test_mixedret_c(
+; CHECK-NEXT: ret i32
+; CHECK: call i32 @test_mixedret_d(i1 zeroext %b)
+; CHECK: add i32 1,
+; CHECK-NOT: br
+; CHECK: ret i32
+
+declare i32 @test_mixedret_c(i1 zeroext %b)
+declare i32 @test_mixedret_d(i1 zeroext %b)
+define internal i32 @test_mixedret_b(i1 zeroext %b) {
+  br i1 %b, label %c, label %d
+c:
+  %c_rv = musttail call i32 @test_mixedret_c(i1 zeroext %b)
+  ret i32 %c_rv
+d:
+  %d_rv = call i32 @test_mixedret_d(i1 zeroext %b)
+  %d_rv1 = add i32 1, %d_rv
+  ret i32 %d_rv1
+}
+define i32 @test_mixedret_a(i1 zeroext %b) {
+  %rv = musttail call i32 @test_mixedret_b(i1 zeroext %b)
+  ret i32 %rv
+}