[llvm] [RISCV] Add CompressPat for c.beqz/bnez with X0 in the first operand. (PR #69042)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

Copy propagation during codegen can cause the first operand to become X0. We should be able to compress that.

---
Full diff: https://github.com/llvm/llvm-project/pull/69042.diff


2 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVInstrInfoC.td (+6) 
- (modified) llvm/test/MC/RISCV/compress-rv32i.s (+24-4) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoC.td b/llvm/lib/Target/RISCV/RISCVInstrInfoC.td
index aff6e77e0cfc480..07137031d9fc712 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoC.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoC.td
@@ -956,8 +956,14 @@ def : CompressPat<(JAL X0, simm12_lsb0:$offset),
                   (C_J simm12_lsb0:$offset)>;
 def : CompressPat<(BEQ GPRC:$rs1, X0, simm9_lsb0:$imm),
                   (C_BEQZ GPRC:$rs1, simm9_lsb0:$imm)>;
+let isCompressOnly = true in
+def : CompressPat<(BEQ X0, GPRC:$rs1, simm9_lsb0:$imm),
+                  (C_BEQZ GPRC:$rs1, simm9_lsb0:$imm)>;
 def : CompressPat<(BNE GPRC:$rs1, X0, simm9_lsb0:$imm),
                   (C_BNEZ GPRC:$rs1, simm9_lsb0:$imm)>;
+let isCompressOnly = true in
+def : CompressPat<(BNE X0, GPRC:$rs1, simm9_lsb0:$imm),
+                  (C_BNEZ GPRC:$rs1, simm9_lsb0:$imm)>;
 } // Predicates = [HasStdExtCOrZca]
 
 // Quadrant 2
diff --git a/llvm/test/MC/RISCV/compress-rv32i.s b/llvm/test/MC/RISCV/compress-rv32i.s
index 7869481bb78d690..165defc3435fcc9 100644
--- a/llvm/test/MC/RISCV/compress-rv32i.s
+++ b/llvm/test/MC/RISCV/compress-rv32i.s
@@ -154,16 +154,36 @@ jal zero, -2048
 # CHECK: # encoding: [0x01,0xd0]
 beq s0, zero, -256
 
+# CHECK-BYTES: 01 d0
+# CHECK-ALIASASM: beqz s0, -256
+# CHECK-ALIASOBJ32: beqz s0, 0xffffff2a
+# CHECK-ALIASOBJ64: beqz s0, 0xffffffffffffff2a
+# CHECK-INSTASM: c.beqz s0, -256
+# CHECK-INSTOBJ32: c.beqz s0, 0xffffff2a
+# CHECK-INSTOBJ64: c.beqz s0, 0xffffffffffffff2a
+# CHECK: # encoding: [0x01,0xd0]
+beq zero, s0, -256
+
 # CHECK-BYTES: 7d ec
 # CHECK-ALIASASM: bnez s0, 254
-# CHECK-ALIASOBJ32: bnez s0, 0x128
-# CHECK-ALIASOBJ64: bnez s0, 0x128
+# CHECK-ALIASOBJ32: bnez s0, 0x12a
+# CHECK-ALIASOBJ64: bnez s0, 0x12a
 # CHECK-INSTASM: c.bnez s0, 254
-# CHECK-INSTOBJ32: c.bnez s0, 0x128
-# CHECK-INSTOBJ64: c.bnez s0, 0x128
+# CHECK-INSTOBJ32: c.bnez s0, 0x12a
+# CHECK-INSTOBJ64: c.bnez s0, 0x12a
 # CHECK: # encoding: [0x7d,0xec]
 bne s0, zero, 254
 
+# CHECK-BYTES: 7d ec
+# CHECK-ALIASASM: bnez s0, 254
+# CHECK-ALIASOBJ32: bnez s0, 0x12c
+# CHECK-ALIASOBJ64: bnez s0, 0x12c
+# CHECK-INSTASM: c.bnez s0, 254
+# CHECK-INSTOBJ32: c.bnez s0, 0x12c
+# CHECK-INSTOBJ64: c.bnez s0, 0x12c
+# CHECK: # encoding: [0x7d,0xec]
+bne zero, s0, 254
+
 # CHECK-BYTES: 7e 04
 # CHECK-ALIAS: slli s0, s0, 31
 # CHECK-INST: c.slli s0, 31

``````````

</details>


https://github.com/llvm/llvm-project/pull/69042