Add 'musttail' marker to call instructions

This is similar to the 'tail' marker, except that it guarantees that
tail call optimization will occur.  It also comes with convervative IR
verification rules that ensure that tail call optimization is possible.

Reviewers: nicholas

Differential Revision: http://llvm-reviews.chandlerc.com/D3240

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207143 91177308-0d34-0410-b5e6-96231b3b80d8

test/Verifier/musttail-invalid.ll

@@ -0,0 +1,75 @@
+; RUN: not llvm-as %s -o /dev/null 2>&1 | FileCheck %s
+
+; Each musttail call should fail to validate.
+
+declare x86_stdcallcc void @cc_mismatch_callee()
+define void @cc_mismatch() {
+; CHECK: mismatched calling conv
+  musttail call x86_stdcallcc void @cc_mismatch_callee()
+  ret void
+}
+
+declare void @more_parms_callee(i32)
+define void @more_parms() {
+; CHECK: mismatched parameter counts
+  musttail call void @more_parms_callee(i32 0)
+  ret void
+}
+
+declare void @mismatched_intty_callee(i8)
+define void @mismatched_intty(i32) {
+; CHECK: mismatched parameter types
+  musttail call void @mismatched_intty_callee(i8 0)
+  ret void
+}
+
+declare void @mismatched_vararg_callee(i8*, ...)
+define void @mismatched_vararg(i8*) {
+; CHECK: mismatched varargs
+  musttail call void (i8*, ...)* @mismatched_vararg_callee(i8* null)
+  ret void
+}
+
+; We would make this an implicit sret parameter, which would disturb the
+; tail call.
+declare { i32, i32, i32 } @mismatched_retty_callee(i32)
+define void @mismatched_retty(i32) {
+; CHECK: mismatched return types
+  musttail call { i32, i32, i32 } @mismatched_retty_callee(i32 0)
+  ret void
+}
+
+declare void @mismatched_byval_callee({ i32 }*)
+define void @mismatched_byval({ i32 }* byval %a) {
+; CHECK: mismatched ABI impacting function attributes
+  musttail call void @mismatched_byval_callee({ i32 }* %a)
+  ret void
+}
+
+declare void @mismatched_inreg_callee(i32 inreg)
+define void @mismatched_inreg(i32 %a) {
+; CHECK: mismatched ABI impacting function attributes
+  musttail call void @mismatched_inreg_callee(i32 inreg %a)
+  ret void
+}
+
+declare void @mismatched_sret_callee(i32* sret)
+define void @mismatched_sret(i32* %a) {
+; CHECK: mismatched ABI impacting function attributes
+  musttail call void @mismatched_sret_callee(i32* sret %a)
+  ret void
+}
+
+declare i32 @not_tail_pos_callee()
+define i32 @not_tail_pos() {
+; CHECK: musttail call must be precede a ret with an optional bitcast
+  %v = musttail call i32 @not_tail_pos_callee()
+  %w = add i32 %v, 1
+  ret i32 %w
+}
+
+define void @inline_asm() {
+; CHECK: cannot use musttail call with inline asm
+  musttail call void asm "ret", ""()
+  ret void
+}

test/Verifier/musttail-valid.ll

@@ -0,0 +1,16 @@
+; RUN: llvm-as %s -o /dev/null
+
+; Should assemble without error.
+
+declare void @similar_param_ptrty_callee(i8*)
+define void @similar_param_ptrty(i32*) {
+  musttail call void @similar_param_ptrty_callee(i8* null)
+  ret void
+}
+
+declare i8* @similar_ret_ptrty_callee()
+define i32* @similar_ret_ptrty() {
+  %v = musttail call i8* @similar_ret_ptrty_callee()
+  %w = bitcast i8* %v to i32*
+  ret i32* %w
+}