[PATCH] D139756: [X86] Fix cmp order in probing BuildStackAlignAND

[Josh Stone via Phabricator via llvm-commits]

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Due to reversed arguments, the loop start was almost always skipping the
whole loop, since FinalStackProbed is probably less than StackPtr for
large alignments. The intent was to skip the loop if the first sub on
StackPtr made it less than FinalStackProbed already, so flip it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D139756

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


Index: llvm/test/CodeGen/X86/stack-clash-small-large-align.ll
===================================================================
--- llvm/test/CodeGen/X86/stack-clash-small-large-align.ll
+++ llvm/test/CodeGen/X86/stack-clash-small-large-align.ll
@@ -40,7 +40,7 @@
 ; CHECK-NEXT:    je .LBB1_4
 ; CHECK-NEXT:  # %bb.1:
 ; CHECK-NEXT:    subq $4096, %rsp # imm = 0x1000
-; CHECK-NEXT:    cmpq %rsp, %r11
+; CHECK-NEXT:    cmpq %r11, %rsp
 ; CHECK-NEXT:    jb .LBB1_3
 ; CHECK-NEXT:  .LBB1_2: # =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    movq $0, (%rsp)
Index: llvm/test/CodeGen/X86/stack-clash-large-large-align.ll
===================================================================
--- llvm/test/CodeGen/X86/stack-clash-large-large-align.ll
+++ llvm/test/CodeGen/X86/stack-clash-large-large-align.ll
@@ -44,7 +44,7 @@
 ; CHECK-NEXT:    je .LBB1_4
 ; CHECK-NEXT:  # %bb.1:
 ; CHECK-NEXT:    subq $4096, %rsp # imm = 0x1000
-; CHECK-NEXT:    cmpq %rsp, %r11
+; CHECK-NEXT:    cmpq %r11, %rsp
 ; CHECK-NEXT:    jb .LBB1_3
 ; CHECK-NEXT:  .LBB1_2: # =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    movq $0, (%rsp)
Index: llvm/lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86FrameLowering.cpp
+++ llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -1293,11 +1293,11 @@
 
         BuildMI(headMBB, DL,
                 TII.get(Uses64BitFramePtr ? X86::CMP64rr : X86::CMP32rr))
-            .addReg(FinalStackProbed)
             .addReg(StackPtr)
+            .addReg(FinalStackProbed)
             .setMIFlag(MachineInstr::FrameSetup);
 
-        // jump
+        // jump to the footer if StackPtr < FinalStackProbed
         BuildMI(headMBB, DL, TII.get(X86::JCC_1))
             .addMBB(footMBB)
             .addImm(X86::COND_B)
@@ -1329,7 +1329,7 @@
             .addReg(StackPtr)
             .setMIFlag(MachineInstr::FrameSetup);
 
-        // jump
+        // jump back while FinalStackProbed < StackPtr
         BuildMI(bodyMBB, DL, TII.get(X86::JCC_1))
             .addMBB(bodyMBB)
             .addImm(X86::COND_B)


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