[llvm] [X86] Recognize POP/ADD/SUB modifying rsp in getSPAdjust. (PR #114265)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Daniel Zabawa (daniel-zabawa)

<details>
<summary>Changes</summary>

This code assumed only PUSHes would appear in call sequences. However, if calls require frame-pointer/base-pointer spills, only the PUSH operations inserted by spillFPBP will be recognized, and the adjustments to frame object offsets in prologepilog will be incorrect.

This change correctly reports the SP adjustment for POP and ADD/SUB to rsp, and an assertion for unrecognized instructions that modify rsp.

There is no unit test provided as the issue can only be reliably reproduced in MIR (to force a spill/restore outside and inside a call sequence, respectively), but MIR cannot serialize the FPClobberedByCall field that triggers spillFPBP to run.

---
Full diff: https://github.com/llvm/llvm-project/pull/114265.diff


1 Files Affected:

- (modified) llvm/lib/Target/X86/X86InstrInfo.cpp (+29-2) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 38ea1f35be2b9a..e2285417a155e4 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -452,10 +452,13 @@ int X86InstrInfo::getSPAdjust(const MachineInstr &MI) const {
     return -(I->getOperand(1).getImm());
   }
 
-  // Currently handle only PUSHes we can reasonably expect to see
-  // in call sequences
+  // Handle other opcodes we reasonably expect to see in call
+  // sequences. Note this may include spill/restore of FP/BP.
   switch (MI.getOpcode()) {
   default:
+    assert(!(MI.modifiesRegister(X86::RSP, &RI) ||
+             MI.getDesc().hasImplicitDefOfPhysReg(X86::RSP)) &&
+           "Unhandled opcode in getSPAdjust");
     return 0;
   case X86::PUSH32r:
   case X86::PUSH32rmm:
@@ -467,6 +470,30 @@ int X86InstrInfo::getSPAdjust(const MachineInstr &MI) const {
   case X86::PUSH64rmr:
   case X86::PUSH64i32:
     return 8;
+  case X86::POP32r:
+  case X86::POP32rmm:
+  case X86::POP32rmr:
+    return -4;
+  case X86::POP64r:
+  case X86::POP64rmm:
+  case X86::POP64rmr:
+    return -8;
+  // FIXME: (implement and) use isAddImmediate in the
+  // default case instead of the following ADD/SUB cases.
+  case X86::ADD32ri:
+  case X86::ADD32ri8:
+  case X86::ADD64ri32:
+    if (MI.getOperand(0).getReg() == X86::RSP &&
+        MI.getOperand(1).getReg() == X86::RSP)
+      return -MI.getOperand(2).getImm();
+    return 0;
+  case X86::SUB32ri:
+  case X86::SUB32ri8:
+  case X86::SUB64ri32:
+    if (MI.getOperand(0).getReg() == X86::RSP &&
+        MI.getOperand(1).getReg() == X86::RSP)
+      return MI.getOperand(2).getImm();
+    return 0;
   }
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/114265