[PATCH] D20406: X86: Don't reset the stack after calls that don't return (PR27117)

[Hans Wennborg via llvm-commits]

hans updated this revision to Diff 57841.
hans added a comment.

Addressing comments.


http://reviews.llvm.org/D20406

Files:
  include/llvm/Target/TargetLowering.h
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/noreturn-call.ll

Index: test/CodeGen/X86/noreturn-call.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/noreturn-call.ll
@@ -0,0 +1,48 @@
+; RUN: llc < %s -mtriple=i686-pc-win32 | FileCheck %s
+
+define void @test1(i32 %c) {
+; CHECK-LABEL: test1:
+entry:
+  %0 = alloca i8, i32 %c
+  %tobool = icmp eq i32 %c, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.end:
+  call void @g(i8* %0)
+  ret void
+
+if.then:
+  call void @crash(i8* %0)
+  unreachable
+; CHECK: calll _crash
+; There is no need to adjust the stack after the call, since
+; the function is noreturn and that code will therefore never run.
+; CHECK-NOT: add
+; CHECK-NOT: pop
+}
+
+define void @test2(i32 %c) {
+; CHECK-LABEL: test2:
+entry:
+  %0 = alloca i8, i32 %c
+  %tobool = icmp eq i32 %c, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.end:
+  call void @g(i8* %0)
+  ret void
+
+if.then:
+  call void @crash2(i8* %0)
+  unreachable
+; CHECK: calll _crash2
+; Even though _crash2 is not marked noreturn, it is in practice because
+; of the "unreachable" right after it. This happens e.g. when falling off
+; a non-void function after a call.
+; CHECK-NOT: add
+; CHECK-NOT: pop
+}
+
+declare void @crash(i8*) noreturn
+declare void @crash2(i8*)
+declare void @g(i8*)
Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -3381,6 +3381,12 @@
   else
     NumBytesForCalleeToPop = 0;  // Callee pops nothing.
 
+  if (CLI.DoesNotReturn && !getTargetMachine().Options.TrapUnreachable) {
+    // No need to reset the stack after the call if the call doesn't return. To
+    // make the MI verify, we'll pretend the callee does it for us.
+    NumBytesForCalleeToPop = NumBytes;
+  }
+
   // Returns a flag for retval copy to use.
   if (!IsSibcall) {
     Chain = DAG.getCALLSEQ_END(Chain,
Index: include/llvm/Target/TargetLowering.h
===================================================================
--- include/llvm/Target/TargetLowering.h
+++ include/llvm/Target/TargetLowering.h
@@ -2520,7 +2520,10 @@
       RetTy = ResultType;
 
       IsInReg = Call.paramHasAttr(0, Attribute::InReg);
-      DoesNotReturn = Call.doesNotReturn();
+      DoesNotReturn =
+          Call.doesNotReturn() ||
+          (!Call.isInvoke() &&
+           isa<UnreachableInst>(Call.getInstruction()->getNextNode()));
       IsVarArg = FTy->isVarArg();
       IsReturnValueUsed = !Call.getInstruction()->use_empty();
       RetSExt = Call.paramHasAttr(0, Attribute::SExt);


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