[stack-clash] Fix probing of dynamic alloca

- Perform the probing in the correct direction.
  Related to https://github.com/rust-lang/rust/pull/77885#issuecomment-711062924

- The first touch on a dynamic alloca cannot use a mov because it clobbers
  existing space. Use a xor 0 instead

Differential Revision: https://reviews.llvm.org/D90216

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index fb9fc84..28f4a3b 100644 (file)
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -32316,7 +32316,7 @@ X86TargetLowering::EmitLoweredProbedAlloca(MachineInstr &MI,
 
   BuildMI(testMBB, DL, TII->get(X86::JCC_1))
       .addMBB(tailMBB)
-      .addImm(X86::COND_LE);
+      .addImm(X86::COND_GE);
   testMBB->addSuccessor(blockMBB);
   testMBB->addSuccessor(tailMBB);
 
@@ -32332,9 +32332,9 @@ X86TargetLowering::EmitLoweredProbedAlloca(MachineInstr &MI,
   //
   // The property we want to enforce is to never have more than [page alloc] between two probes.
 
-  const unsigned MovMIOpc =
-      TFI.Uses64BitFramePtr ? X86::MOV64mi32 : X86::MOV32mi;
-  addRegOffset(BuildMI(blockMBB, DL, TII->get(MovMIOpc)), physSPReg, false, 0)
+  const unsigned XORMIOpc =
+      TFI.Uses64BitFramePtr ? X86::XOR64mi8 : X86::XOR32mi8;
+  addRegOffset(BuildMI(blockMBB, DL, TII->get(XORMIOpc)), physSPReg, false, 0)
       .addImm(0);
 
   BuildMI(blockMBB, DL,

diff --git a/llvm/test/CodeGen/X86/stack-clash-dynamic-alloca.ll b/llvm/test/CodeGen/X86/stack-clash-dynamic-alloca.ll
index 82fd678..6dd8b6a 100644 (file)
--- a/llvm/test/CodeGen/X86/stack-clash-dynamic-alloca.ll
+++ b/llvm/test/CodeGen/X86/stack-clash-dynamic-alloca.ll
@@ -24,12 +24,12 @@ attributes #0 =  {"probe-stack"="inline-asm"}
 ; CHECK-X86-64-NEXT:   andq    $-16, %rcx
 ; CHECK-X86-64-NEXT:   subq    %rcx, %rax
 ; CHECK-X86-64-NEXT:   cmpq    %rsp, %rax
-; CHECK-X86-64-NEXT:   jle     .LBB0_3
+; CHECK-X86-64-NEXT:   jge     .LBB0_3
 ; CHECK-X86-64-NEXT:  .LBB0_2: # =>This Inner Loop Header: Depth=1
-; CHECK-X86-64-NEXT:   movq    $0, (%rsp)
+; CHECK-X86-64-NEXT:   xorq    $0, (%rsp)
 ; CHECK-X86-64-NEXT:   subq    $4096, %rsp # imm = 0x1000
 ; CHECK-X86-64-NEXT:   cmpq    %rsp, %rax
-; CHECK-X86-64-NEXT:   jg      .LBB0_2
+; CHECK-X86-64-NEXT:   jl      .LBB0_2
 ; CHECK-X86-64-NEXT:  .LBB0_3:
 ; CHECK-X86-64-NEXT:   movq    %rax, %rsp
 ; CHECK-X86-64-NEXT:   movl    $1, 4792(%rax)
@@ -54,12 +54,12 @@ attributes #0 =  {"probe-stack"="inline-asm"}
 ; CHECK-X86-32-NEXT:    andl    $-16, %ecx
 ; CHECK-X86-32-NEXT:    subl    %ecx, %eax
 ; CHECK-X86-32-NEXT:    cmpl    %esp, %eax
-; CHECK-X86-32-NEXT:    jle  .LBB0_3
+; CHECK-X86-32-NEXT:    jge  .LBB0_3
 ; CHECK-X86-32-NEXT:  .LBB0_2: # =>This Inner Loop Header: Depth=1
-; CHECK-X86-32-NEXT:    movl    $0, (%esp)
+; CHECK-X86-32-NEXT:    xorl    $0, (%esp)
 ; CHECK-X86-32-NEXT:    subl    $4096, %esp # imm = 0x1000
 ; CHECK-X86-32-NEXT:    cmpl    %esp, %eax
-; CHECK-X86-32-NEXT:    jg .LBB0_2
+; CHECK-X86-32-NEXT:    jl .LBB0_2
 ; CHECK-X86-32-NEXT:  .LBB0_3:
 ; CHECK-X86-32-NEXT:    movl    %eax, %esp
 ; CHECK-X86-32-NEXT:    movl    $1, 4792(%eax)

diff --git a/llvm/test/CodeGen/X86/stack-clash-small-alloc-medium-align.ll b/llvm/test/CodeGen/X86/stack-clash-small-alloc-medium-align.ll
index eafa86f..39b6c36 100644 (file)
--- a/llvm/test/CodeGen/X86/stack-clash-small-alloc-medium-align.ll
+++ b/llvm/test/CodeGen/X86/stack-clash-small-alloc-medium-align.ll
@@ -106,12 +106,12 @@ define i32 @foo4(i64 %i) local_unnamed_addr #0 {
 ; CHECK-NEXT:  andq    $-16, %rcx
 ; CHECK-NEXT:  subq    %rcx, %rax
 ; CHECK-NEXT:  cmpq    %rsp, %rax
-; CHECK-NEXT:  jle     .LBB3_3
+; CHECK-NEXT:  jge     .LBB3_3
 ; CHECK-NEXT:.LBB3_2:                                # =>This Inner Loop Header: Depth=1
-; CHECK-NEXT:  movq    $0, (%rsp)
+; CHECK-NEXT:  xorq    $0, (%rsp)
 ; CHECK-NEXT:  subq    $4096, %rsp                     # imm = 0x1000
 ; CHECK-NEXT:  cmpq    %rsp, %rax
-; CHECK-NEXT:  jg      .LBB3_2
+; CHECK-NEXT:  jl      .LBB3_2
 ; CHECK-NEXT:.LBB3_3:
 ; CHECK-NEXT:  andq    $-64, %rax
 ; CHECK-NEXT:  movq    %rax, %rsp