From: Oliver Stannard <oliver.stannard@linaro.org>
Date: Tue, 3 Sep 2019 09:51:19 +0000 (+0000)
Subject: Bug fix on function epilog optimization (ARM backend)
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2536f8c7737db112d564966486b4cf0431135fac;p=llvm

Bug fix on function epilog optimization (ARM backend)

To save a 'add sp,#val' instruction by adding registers to the final pop instruction,
the first register transferred by this pop instruction need to be found.
If the function to be optimized has a non-void return value, the operand list contains
r0 (implicit) which prevents the optimization to take place.
Therefore implicit register references should be skipped in the search loop,
because this registers are never popped from the stack.

Patch by Rainer Herbertz (rOptimizer)!

Differential revision: https://reviews.llvm.org/D66730

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@370728 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index d166a6d7eeb..680729dd29b 100644
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -2420,7 +2420,8 @@ bool llvm::tryFoldSPUpdateIntoPushPop(const ARMSubtarget &Subtarget,
     MachineOperand &MO = MI->getOperand(i);
     RegList.push_back(MO);
 
-    if (MO.isReg() && TRI->getEncodingValue(MO.getReg()) < FirstRegEnc)
+    if (MO.isReg() && !MO.isImplicit() &&
+        TRI->getEncodingValue(MO.getReg()) < FirstRegEnc)
       FirstRegEnc = TRI->getEncodingValue(MO.getReg());
   }
 
@@ -2430,7 +2431,7 @@ bool llvm::tryFoldSPUpdateIntoPushPop(const ARMSubtarget &Subtarget,
   for (int CurRegEnc = FirstRegEnc - 1; CurRegEnc >= 0 && RegsNeeded;
        --CurRegEnc) {
     unsigned CurReg = RegClass->getRegister(CurRegEnc);
-    if (IsT1PushPop && CurReg > ARM::R7)
+    if (IsT1PushPop && CurRegEnc > TRI->getEncodingValue(ARM::R7))
       continue;
     if (!IsPop) {
       // Pushing any register is completely harmless, mark the register involved
diff --git a/test/CodeGen/ARM/fold-stack-adjust.ll b/test/CodeGen/ARM/fold-stack-adjust.ll
index b8ff910fd17..6256138e9a0 100644
--- a/test/CodeGen/ARM/fold-stack-adjust.ll
+++ b/test/CodeGen/ARM/fold-stack-adjust.ll
@@ -42,6 +42,19 @@ define void @check_simple() minsize {
   ret void
 }
 
+define i32 @check_simple_ret() minsize {
+; CHECK-FNSTART-LABEL: check_simple_ret:
+; CHECK: push {r5, r6, r7, lr}
+; CHECK-NOT: sub sp,
+; ...
+; CHECK-NOT: add sp,
+; CHECK: pop {r2, r3, r7, pc}
+
+  %var = alloca i8, i32 8
+  call void @bar(i8* %var)
+  ret i32 0
+}
+
 define void @check_simple_too_big() minsize {
 ; CHECK-FNSTART-LABEL: check_simple_too_big:
 ; CHECK: push {r7, lr}