[llvm] abb18dd - X86: Remove LOW32_ADDR_ACCESS_RBPRegClass (#155127)

[via llvm-commits]

Author: Matt Arsenault
Date: 2025-08-26T23:58:05+09:00
New Revision: abb18ddc9c3f2f85f1fcbefc25529ed22e84a680

URL: https://github.com/llvm/llvm-project/commit/abb18ddc9c3f2f85f1fcbefc25529ed22e84a680
DIFF: https://github.com/llvm/llvm-project/commit/abb18ddc9c3f2f85f1fcbefc25529ed22e84a680.diff

LOG: X86: Remove LOW32_ADDR_ACCESS_RBPRegClass (#155127)

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86RegisterInfo.cpp
    llvm/lib/Target/X86/X86RegisterInfo.td

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index 595ad3290eedb..b79e508df7c97 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -204,15 +204,7 @@ X86RegisterInfo::getPointerRegClass(const MachineFunction &MF,
     // we can still use 64-bit register as long as we know the high bits
     // are zeros.
     // Reflect that in the returned register class.
-    if (Is64Bit) {
-      // When the target also allows 64-bit frame pointer and we do have a
-      // frame, this is fine to use it for the address accesses as well.
-      const X86FrameLowering *TFI = getFrameLowering(MF);
-      return TFI->hasFP(MF) && TFI->Uses64BitFramePtr
-                 ? &X86::LOW32_ADDR_ACCESS_RBPRegClass
-                 : &X86::LOW32_ADDR_ACCESSRegClass;
-    }
-    return &X86::GR32RegClass;
+    return Is64Bit ? &X86::LOW32_ADDR_ACCESSRegClass : &X86::GR32RegClass;
   case 1: // Normal GPRs except the stack pointer (for encoding reasons).
     if (Subtarget.isTarget64BitLP64())
       return &X86::GR64_NOSPRegClass;

diff  --git a/llvm/lib/Target/X86/X86RegisterInfo.td b/llvm/lib/Target/X86/X86RegisterInfo.td
index e9ca25d808a56..99b7910131dc5 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.td
+++ b/llvm/lib/Target/X86/X86RegisterInfo.td
@@ -716,10 +716,7 @@ def GR64_NOREX2_NOSP : RegisterClass<"X86", [i64], 64,
 // which we do not have right now.
 def LOW32_ADDR_ACCESS : RegisterClass<"X86", [i32], 32, (add GR32, RIP)>;
 
-// When RBP is used as a base pointer in a 32-bit addresses environment,
-// this is also safe to use the full register to access addresses.
-// Since RBP will never be spilled, stick to a 32 alignment to save
-// on memory consumption.
+// FIXME: This is unused, but deleting it results in codegen changes
 def LOW32_ADDR_ACCESS_RBP : RegisterClass<"X86", [i32], 32,
                                           (add LOW32_ADDR_ACCESS, RBP)>;