[PATCH] D82867: Fix tail allocation for large static alloca

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serge-sans-paille created this revision.
serge-sans-paille added a reviewer: craig.topper.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
serge-sans-paille marked an inline comment as done.
serge-sans-paille added inline comments.


================
Comment at: llvm/test/CodeGen/X86/stack-clash-large.ll:46
 ; CHECK-X86-32-NEXT:# %bb.2:
-; CHECK-X86-32-NEXT:    movl    %r11d, %esp
 ; CHECK-X86-32-NEXT:    .cfi_def_cfa_offset 72016
----------------
This `mov` wasn't relevant, as `%r11d` was clipped.


https://reviews.llvm.org/D82867

Files:
  llvm/lib/Target/X86/X86FrameLowering.cpp
  llvm/test/CodeGen/X86/stack-clash-large.ll


Index: llvm/test/CodeGen/X86/stack-clash-large.ll
===================================================================
--- llvm/test/CodeGen/X86/stack-clash-large.ll
+++ llvm/test/CodeGen/X86/stack-clash-large.ll
@@ -24,7 +24,7 @@
 ; CHECK-X86-64-NEXT:	cmpq	%r11, %rsp
 ; CHECK-X86-64-NEXT:	jl	.LBB0_1
 ; CHECK-X86-64-NEXT:# %bb.2:
-; CHECK-X86-64-NEXT:	movq    %r11, %rsp
+; CHECK-X86-64-NEXT:	subq    $2248, %rsp
 ; CHECK-X86-64-NEXT:	.cfi_def_cfa_offset 71888
 ; CHECK-X86-64-NEXT:	movl	$1, 264(%rsp)
 ; CHECK-X86-64-NEXT:	movl	$1, 28664(%rsp)
@@ -43,7 +43,7 @@
 ; CHECK-X86-32-NEXT:    cmpl    %r11d, %esp
 ; CHECK-X86-32-NEXT:    jl  .LBB0_1
 ; CHECK-X86-32-NEXT:# %bb.2:
-; CHECK-X86-32-NEXT:    movl    %r11d, %esp
+; CHECK-X86-32-NEXT:    subl    $2380, %esp
 ; CHECK-X86-32-NEXT:    .cfi_def_cfa_offset 72016
 ; CHECK-X86-32-NEXT:    movl    $1, 392(%esp)
 ; CHECK-X86-32-NEXT:    movl    $1, 28792(%esp)
Index: llvm/lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86FrameLowering.cpp
+++ llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -686,10 +686,12 @@
   MBB.addSuccessor(testMBB);
 
   // handle tail
-  if (Offset % StackProbeSize) {
-    BuildMI(*tailMBB, tailMBB->begin(), DL, TII.get(TargetOpcode::COPY),
-            StackPtr)
-        .addReg(FinalStackPtr)
+  unsigned TailOffset = Offset % StackProbeSize;
+  if (TailOffset) {
+    const unsigned Opc = getSUBriOpcode(Uses64BitFramePtr, TailOffset);
+    BuildMI(*tailMBB, tailMBB->begin(), DL, TII.get(Opc), StackPtr)
+        .addReg(StackPtr)
+        .addImm(TailOffset)
         .setMIFlag(MachineInstr::FrameSetup);
   }
 


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