[ARM] Don't try to create "push {r12, lr}" in Thumb1 at -Oz.

[efriedma]

Summary

It's a little tricky to make this issue show up because prologue/epilogue emission normally likes to push at least two registers... but it doesn't when lr is force-spilled due to function length. Not sure if that really makes sense, but I decided not to touch it for now.

[dmgreen]

I don't pretend to know a huge amount about the frame lowering code, but this looks fine to me.

When I tried your example it was pushing r7 and popping r3. I presume this is OK, providing r7 isn't modified?

There are now machine verifier checks for these illegal push/pops, right? Please add -verify-machineinstrs to the tests.

[efriedma]

When I tried your example it was pushing r7 and popping r3. I presume this is OK, providing r7 isn't modified?

Yes; the entire point of tryFoldSPUpdateIntoPushPop is to fold a stack adjustment into a preceding push, possibly using the "wrong" register, to save an instruction.

I'll post a new version with the test fixed.

[efriedma]

Update test to use -verify-machineinstrs, and to use CHECK-LABEL in a way that's less likely to cause confusion.

[dmgreen]

LGTM

lib/Target/ARM/ARMBaseInstrInfo.cpp

bool llvm::tryFoldSPUpdateIntoPushPop(const ARMSubtarget &Subtarget,
   }
 
   const MCPhysReg *CSRegs = TRI->getCalleeSavedRegs(&MF);
 
   // Now try to find enough space in the reglist to allocate NumBytes.
   for (int CurRegEnc = FirstRegEnc - 1; CurRegEnc >= 0 && RegsNeeded;
        --CurRegEnc) {
     unsigned CurReg = RegClass->getRegister(CurRegEnc);
+    if (IsT1PushPop && CurReg > ARM::R7)
+      continue;
     if (!IsPop) {
       // Pushing any register is completely harmless, mark the register involved
       // as undef since we don't care about its value and must not restore it
       // during stack unwinding.
       RegList.push_back(MachineOperand::CreateReg(CurReg, false, false,
                                                   false, false, true));
       --RegsNeeded;
       continue;

test/CodeGen/ARM/fold-stack-adjust.ll

 ; Disable shrink-wrapping on the first test otherwise we wouldn't
 ; exerce the path for PR18136.
-; RUN: llc -mtriple=thumbv7-apple-none-macho < %s -enable-shrink-wrap=false | FileCheck %s
-; RUN: llc -mtriple=thumbv6m-apple-none-macho -frame-pointer=all < %s | FileCheck %s --check-prefix=CHECK-T1
-; RUN: llc -mtriple=thumbv7-apple-darwin-ios -frame-pointer=all < %s | FileCheck %s --check-prefix=CHECK-IOS
-; RUN: llc -mtriple=thumbv7--linux-gnueabi -frame-pointer=all < %s | FileCheck %s --check-prefix=CHECK-LINUX
-
+; RUN: llc -mtriple=thumbv7-apple-none-macho < %s -enable-shrink-wrap=false -verify-machineinstrs | FileCheck %s --check-prefixes=CHECK-FNSTART,CHECK
+; RUN: llc -mtriple=thumbv6m-apple-none-macho -frame-pointer=all < %s -verify-machineinstrs | FileCheck %s --check-prefixes=CHECK-FNSTART,CHECK-T1
+; RUN: llc -mtriple=thumbv6m-apple-none-macho < %s -verify-machineinstrs | FileCheck %s --check-prefixes=CHECK-FNSTART,CHECK-T1-NOFP
+; RUN: llc -mtriple=thumbv7-apple-darwin-ios -frame-pointer=all < %s -verify-machineinstrs | FileCheck %s --check-prefixes=CHECK-FNSTART,CHECK-IOS
+; RUN: llc -mtriple=thumbv7--linux-gnueabi -frame-pointer=all < %s -verify-machineinstrs | FileCheck %s --check-prefixes=CHECK-FNSTART,CHECK-LINUX
 
 declare void @bar(i8*)
 
 %bigVec = type [2 x double]
 
 @var = global %bigVec zeroinitializer
 
 define void @check_simple() minsize {
-; CHECK-LABEL: check_simple:
+; CHECK-FNSTART-LABEL: check_simple:
 ; CHECK: push {r3, r4, r5, r6, r7, lr}
 ; CHECK-NOT: sub sp, sp,
 ; ...
 ; CHECK-NOT: add sp, sp,
 ; CHECK: pop {r0, r1, r2, r3, r7, pc}
 
-; CHECK-T1-LABEL: check_simple:
 ; CHECK-T1: push {r3, r4, r5, r6, r7, lr}
 ; CHECK-T1: add r7, sp, #16
 ; CHECK-T1-NOT: sub sp, sp,
 ; ...
 ; CHECK-T1-NOT: add sp, sp,
 ; CHECK-T1: pop {r0, r1, r2, r3, r7, pc}
 
   ; iOS always has a frame pointer and messing with the push affects
   ; how it's set in the prologue. Make sure we get that right.
-; CHECK-IOS-LABEL: check_simple:
 ; CHECK-IOS: push {r3, r4, r5, r6, r7, lr}
 ; CHECK-NOT: sub sp,
 ; CHECK-IOS: add r7, sp, #16
 ; CHECK-NOT: sub sp,
 ; ...
 ; CHECK-NOT: add sp,
 ; CHEC: pop {r3, r4, r5, r6, r7, pc}
 
   %var = alloca i8, i32 16
   call void @bar(i8* %var)
   ret void
 }
 
 define void @check_simple_too_big() minsize {
-; CHECK-LABEL: check_simple_too_big:
+; CHECK-FNSTART-LABEL: check_simple_too_big:
 ; CHECK: push {r7, lr}
 ; CHECK: sub sp,
 ; ...
 ; CHECK: add sp,
 ; CHECK: pop {r7, pc}
   %var = alloca i8, i32 64
   call void @bar(i8* %var)
   ret void
 }
 
 define void @check_vfp_fold() minsize {
-; CHECK-LABEL: check_vfp_fold:
+; CHECK-FNSTART-LABEL: check_vfp_fold:
 ; CHECK: push {r[[GLOBREG:[0-9]+]], lr}
 ; CHECK: vpush {d6, d7, d8, d9}
 ; CHECK-NOT: sub sp,
 ; ...
 ; CHECK-NOT: add sp,
 ; CHECK: vpop {d6, d7, d8, d9}
 ; CHECK: pop {r[[GLOBREG]], pc}
 
   ; iOS uses aligned NEON stores here, which is convenient since we
   ; want to make sure that works too.
-; CHECK-IOS-LABEL: check_vfp_fold:
 ; CHECK-IOS: push {r4, r7, lr}
 ; CHECK-IOS: sub.w r4, sp, #16
 ; CHECK-IOS: bfc r4, #0, #4
 ; CHECK-IOS: mov sp, r4
 ; CHECK-IOS: vst1.64 {d8, d9}, [r4:128]
 ; CHECK-IOS: sub sp, #16
 ; ...
 ; CHECK-IOS: add r4, sp, #16
 ; CHECK-IOS: vld1.64 {d8, d9}, [r4:128]
 ; CHECK-IOS: mov sp, r4
 ; CHECK-IOS: pop {r4, r7, pc}
 
   %var = alloca i8, i32 16
 
   call void asm "", "r,~{d8},~{d9}"(i8* %var)
   call void @bar(i8* %var)
 
   ret void
 }
 
 ; This function should use just enough space that the "add sp, sp, ..." could be
 ; folded in except that doing so would clobber the value being returned.
 define i64 @check_no_return_clobber() minsize {
-; CHECK-LABEL: check_no_return_clobber:
+; CHECK-FNSTART-LABEL: check_no_return_clobber:
 ; CHECK: push {r1, r2, r3, r4, r5, r6, r7, lr}
 ; CHECK-NOT: sub sp,
 ; ...
 ; CHECK: add sp, #24
 ; CHECK: pop {r7, pc}
 
-  ; Just to keep iOS FileCheck within previous function:
-; CHECK-IOS-LABEL: check_no_return_clobber:
-
   %var = alloca i8, i32 20
   call void @bar(i8* %var)
   ret i64 0
 }
 
 define arm_aapcs_vfpcc double @check_vfp_no_return_clobber() minsize {
-; CHECK-LABEL: check_vfp_no_return_clobber:
+; CHECK-FNSTART-LABEL: check_vfp_no_return_clobber:
 ; CHECK: push {r[[GLOBREG:[0-9]+]], lr}
 ; CHECK: vpush {d0, d1, d2, d3, d4, d5, d6, d7, d8, d9}
 ; CHECK-NOT: sub sp,
 ; ...
 ; CHECK: add sp, #64
 ; CHECK: vpop {d8, d9}
 ; CHECK: pop {r[[GLOBREG]], pc}
 
   %var = alloca i8, i32 64
 
   %tmp = load %bigVec, %bigVec* @var
   call void @bar(i8* %var)
   store %bigVec %tmp, %bigVec* @var
 
   ret double 1.0
 }
 
 @dbl = global double 0.0
 
 ; PR18136: there was a bug determining where the first eligible pop in a
 ; basic-block was when the entire block was epilogue code.
 define void @test_fold_point(i1 %tst) minsize {
-; CHECK-LABEL: test_fold_point:
+; CHECK-FNSTART-LABEL: test_fold_point:
 
   ; Important to check for beginning of basic block, because if it gets
   ; if-converted the test is probably no longer checking what it should.
 ; CHECK: %end
 ; CHECK-NEXT: vpop {d7, d8}
 ; CHECK-NEXT: pop {r4, pc}
 
   ; With a guaranteed frame-pointer, we want to make sure that its offset in the
   ; push block is correct, even if a few registers have been tacked onto a later
   ; vpush (PR18160).
-; CHECK-IOS-LABEL: test_fold_point:
 ; CHECK-IOS: push {r4, r7, lr}
 ; CHECK-IOS-NEXT: add r7, sp, #4
 ; CHECK-IOS-NEXT: vpush {d7, d8}
 
   ; We want some memory so there's a stack adjustment to fold...
   %var = alloca i8, i32 8
 
   ; We want a long-lived floating register so that a callee-saved dN is used and
   ; there's both a vpop and a pop.
   %live_val = load double, double* @dbl
   br i1 %tst, label %true, label %end
 true:
   call void @bar(i8* %var)
   store double %live_val, double* @dbl
   br label %end
 end:
   ; We want the epilogue to be the only thing in a basic block so that we hit
   ; the correct edge-case (first inst in block is correct one to adjust).
   ret void
 }
 
 define void @test_varsize(...) minsize {
-; CHECK-T1-LABEL: test_varsize:
+; CHECK-FNSTART-LABEL: test_varsize:
 ; CHECK-T1: sub sp, #16
 ; CHECK-T1: push  {r5, r6, r7, lr}
 ; ...
 ; CHECK-T1: pop {r2, r3, r7}
 ; CHECK-T1: pop {[[POP_REG:r[0-3]]]}
 ; CHECK-T1: add sp, #16
 ; CHECK-T1: bx  [[POP_REG]]
 
-; CHECK-LABEL: test_varsize:
 ; CHECK: sub  sp, #16
 ; CHECK: push {r5, r6, r7, lr}
 ; ...
 ; CHECK: pop.w  {r2, r3, r7, lr}
 ; CHECK: add  sp, #16
 ; CHECK: bx lr
 
   %var = alloca i8, i32 8
   call void @llvm.va_start(i8* %var)
   call void @bar(i8* %var)
   ret void
 }
 
 %"MyClass" = type { i8*, i32, i32, float, float, float, [2 x i8], i32, i32* }
 
 declare float @foo()
 
 declare void @bar3()
 
 declare %"MyClass"* @bar2(%"MyClass"* returned, i16*, i32, float, float, i32, i32, i1 zeroext, i1 zeroext, i32)
 
 define fastcc float @check_vfp_no_return_clobber2(i16* %r, i16* %chars, i32 %length, i1 zeroext %flag) minsize {
 entry:
-; CHECK-LINUX-LABEL: check_vfp_no_return_clobber2
+; CHECK-FNSTART-LABEL: check_vfp_no_return_clobber2
 ; CHECK-LINUX: vpush  {d0, d1, d2, d3, d4, d5, d6, d7, d8}
 ; CHECK-NOT: sub sp,
 ; ...
 ; CHECK-LINUX: add sp
 ; CHECK-LINUX: vpop {d8}
   %run = alloca %"MyClass", align 4
   %call = call %"MyClass"* @bar2(%"MyClass"* %run, i16* %chars, i32 %length, float 0.000000e+00, float 0.000000e+00, i32 1, i32 1, i1 zeroext false, i1 zeroext true, i32 3)
   %call1 = call float @foo()
   %cmp = icmp eq %"MyClass"* %run, null
   br i1 %cmp, label %exit, label %if.then
 
 if.then:                                          ; preds = %entry
   call void @bar3()
   br label %exit
 
 exit:                                             ; preds = %if.then, %entry
   ret float %call1
 }
 
 declare void @use_arr(i32*)
 define void @test_fold_reuse() minsize {
-; CHECK-LABEL: test_fold_reuse:
+; CHECK-FNSTART-LABEL: test_fold_reuse:
 ; CHECK: push.w {r4, r7, r8, lr}
 ; CHECK: sub sp, #24
 ; [...]
 ; CHECK: add sp, #24
 ; CHECK: pop.w {r4, r7, r8, pc}
   %arr = alloca i8, i32 24
   call void asm sideeffect "", "~{r8},~{r4}"()
   call void @bar(i8* %arr)
   ret void
 }
 
+; It doesn't matter what registers this pushes and pops; just make sure
+; it doesn't try to push/pop an illegal register on Thumb1.
+define void @test_long_fn() minsize nounwind optsize {
+; CHECK-FNSTART-LABEL: test_long_fn:
+; CHECK-T1-NOFP: push {r7, lr}
+; CHECK-T1-NOFP: pop {r3, pc}
+entry:
+  %z = alloca i32, align 4
+  call void asm sideeffect ".space 3000", "r"(i32* nonnull %z)
+  ret void
+}
+
 declare void @llvm.va_start(i8*) nounwind