Re-land "Avoid emitting unreachable SP adjustments after throw"

This reverts commit 4e0fe03. Re-lands
65b2128.

After landing 5ff5ddd to add int3 into
trailing unreachable blocks, we can now remove these extra stack
adjustments without confusing the Win64 unwinder. See
https://llvm.org/45064#c4 or X86AvoidTrailingCall.cpp for a full
explanation.

Fixes PR45064.

llvm/lib/Target/X86/X86FrameLowering.cpp

@@ -2989,6 +2989,12 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
   I = MBB.erase(I);
   auto InsertPos = skipDebugInstructionsForward(I, MBB.end());
 
+  // Try to avoid emitting dead SP adjustments if the block end is unreachable,
+  // typically because the function is marked noreturn (abort, throw,
+  // assert_fail, etc).
+  if (isDestroy && blockEndIsUnreachable(MBB, I))
+    return I;
+
   if (!reserveCallFrame) {
     // If the stack pointer can be changed after prologue, turn the
     // adjcallstackup instruction into a 'sub ESP, <amt>' and the
@@ -3070,13 +3076,7 @@ eliminateCallFramePseudoInstr(MachineFunction &MF, MachineBasicBlock &MBB,
     return I;
   }
 
-  if (isDestroy && InternalAmt && !blockEndIsUnreachable(MBB, I)) {
-    // If we are performing frame pointer elimination and if the callee pops
-    // something off the stack pointer, add it back.  We do this until we have
-    // more advanced stack pointer tracking ability.
-    // We are not tracking the stack pointer adjustment by the callee, so make
-    // sure we restore the stack pointer immediately after the call, there may
-    // be spill code inserted between the CALL and ADJCALLSTACKUP instructions.
+  if (InternalAmt) {
     MachineBasicBlock::iterator CI = I;
     MachineBasicBlock::iterator B = MBB.begin();
     while (CI != B && !std::prev(CI)->isCall())

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -4366,12 +4366,6 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   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,

llvm/test/CodeGen/X86/noreturn-call-win64.ll

@@ -1,5 +1,8 @@
 ; RUN: llc < %s -mtriple=x86_64-windows-msvc | FileCheck %s
 
+%struct.MakeCleanup = type { i8 }
+%eh.ThrowInfo = type { i32, i32, i32, i32 }
+
 ; Function Attrs: noinline nounwind optnone uwtable
 define dso_local i32 @foo() {
 entry:
@@ -51,3 +54,60 @@ declare dso_local i32 @cond()
 declare dso_local void @abort1() noreturn
 declare dso_local void @abort2() noreturn
 declare dso_local void @abort3() noreturn
+
+define dso_local void @throw_exception() uwtable personality i32 (...)* @__CxxFrameHandler3 {
+entry:
+  %o = alloca %struct.MakeCleanup, align 1
+  %call = invoke i32 @cond()
+          to label %invoke.cont unwind label %ehcleanup
+
+invoke.cont:                                      ; preds = %entry
+  %cmp1 = icmp eq i32 0, %call
+  br i1 %cmp1, label %if.then, label %if.end
+
+if.then:                                          ; preds = %invoke.cont
+  invoke void @_CxxThrowException(i8* null, %eh.ThrowInfo* null)
+          to label %unreachable unwind label %ehcleanup
+
+if.end:                                           ; preds = %invoke.cont
+  %call2 = invoke i32 @cond()
+          to label %invoke.cont1 unwind label %ehcleanup
+
+invoke.cont1:                                     ; preds = %if.end
+  %cmp2 = icmp eq i32 0, %call2
+  br i1 %cmp2, label %if.then3, label %if.end4
+
+if.then3:                                         ; preds = %invoke.cont1
+  invoke void @_CxxThrowException(i8* null, %eh.ThrowInfo* null)
+          to label %unreachable unwind label %ehcleanup
+
+if.end4:                                          ; preds = %invoke.cont1
+  call void @"??1MakeCleanup@@QEAA@XZ"(%struct.MakeCleanup* nonnull %o)
+  ret void
+
+ehcleanup:                                        ; preds = %if.then3, %if.end, %if.then, %entry
+  %cp = cleanuppad within none []
+  call void @"??1MakeCleanup@@QEAA@XZ"(%struct.MakeCleanup* nonnull %o) [ "funclet"(token %cp) ]
+  cleanupret from %cp unwind to caller
+
+unreachable:                                      ; preds = %if.then3, %if.then
+  unreachable
+}
+
+declare dso_local i32 @__CxxFrameHandler3(...)
+declare dso_local void @_CxxThrowException(i8*, %eh.ThrowInfo*)
+declare dso_local void @"??1MakeCleanup@@QEAA@XZ"(%struct.MakeCleanup*)
+
+; CHECK-LABEL: throw_exception:
+; CHECK: callq cond
+; CHECK: je
+; CHECK: callq cond
+; CHECK: je
+; CHECK: retq
+; CHECK: callq _CxxThrowException
+; CHECK-NOT: {{(addq|subq) .*, %rsp}}
+; CHECK: callq _CxxThrowException
+; CHECK-NOT: {{(addq|subq) .*, %rsp}}
+; CHECK: # %unreachable
+; CHECK: int3
+; CHECK: .seh_handlerdata