[llvm] [RISCV] Avoid using x7/t2 for indirect branches which need landing pad. (PR #68292)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

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

<details>
<summary>Changes</summary>

When Zicfilp enabled, this avoids selecting brind to PseudoBRIND, since PseudoBRIND may uses X7 as rs1 and be identified as a software guarded jump. There is an another PR #<!-- -->66762 to use software guarded jump for jumptable branch.

---
Full diff: https://github.com/llvm/llvm-project/pull/68292.diff


4 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVFeatures.td (+2) 
- (modified) llvm/lib/Target/RISCV/RISCVInstrInfo.td (+16) 
- (modified) llvm/lib/Target/RISCV/RISCVRegisterInfo.td (+2) 
- (added) llvm/test/CodeGen/RISCV/zicfilp-brind.ll (+49) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVFeatures.td b/llvm/lib/Target/RISCV/RISCVFeatures.td
index 3d3486b7fa89563..7ba09d65e54d136 100644
--- a/llvm/lib/Target/RISCV/RISCVFeatures.td
+++ b/llvm/lib/Target/RISCV/RISCVFeatures.td
@@ -672,6 +672,8 @@ def FeatureStdExtZicfilp
 def HasStdExtZicfilp : Predicate<"Subtarget->hasStdExtZicfilp()">,
                                  AssemblerPredicate<(all_of FeatureStdExtZicfilp),
                                  "'Zicfilp' (Landing pad)">;
+def NoStdExtZicfilp : Predicate<"!Subtarget->hasStdExtZicfilp()">,
+                                 AssemblerPredicate<(all_of (not FeatureStdExtZicfilp))>;
 
 def FeatureStdExtZicond
     : SubtargetFeature<"experimental-zicond", "HasStdExtZicond", "true",
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.td b/llvm/lib/Target/RISCV/RISCVInstrInfo.td
index abbeff78b6e2864..175b0e3a722cf07 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.td
@@ -1641,9 +1641,25 @@ let isBarrier = 1, isBranch = 1, isIndirectBranch = 1, isTerminator = 1 in
 def PseudoBRIND : Pseudo<(outs), (ins GPRJALR:$rs1, simm12:$imm12), []>,
                   PseudoInstExpansion<(JALR X0, GPR:$rs1, simm12:$imm12)>;
 
+let Predicates = [HasStdExtZicfilp],
+    isBarrier = 1, isBranch = 1, isIndirectBranch = 1, isTerminator = 1 in {
+def PseudoBRINDNonX7 : Pseudo<(outs), (ins GPRJALRNonX7:$rs1, simm12:$imm12), []>,
+                       PseudoInstExpansion<(JALR X0, GPR:$rs1, simm12:$imm12)>;
+}
+
+// For Zicfilp, need to avoid using X7/T2 for indirect branches which need
+// landing pad.
+let Predicates = [HasStdExtZicfilp] in {
+def : Pat<(brind GPRJALRNonX7:$rs1), (PseudoBRINDNonX7 GPRJALRNonX7:$rs1, 0)>;
+def : Pat<(brind (add GPRJALRNonX7:$rs1, simm12:$imm12)),
+          (PseudoBRINDNonX7 GPRJALRNonX7:$rs1, simm12:$imm12)>;
+}
+
+let Predicates = [NoStdExtZicfilp] in {
 def : Pat<(brind GPRJALR:$rs1), (PseudoBRIND GPRJALR:$rs1, 0)>;
 def : Pat<(brind (add GPRJALR:$rs1, simm12:$imm12)),
           (PseudoBRIND GPRJALR:$rs1, simm12:$imm12)>;
+}
 
 // PseudoCALLReg is a generic pseudo instruction for calls which will eventually
 // expand to auipc and jalr while encoding, with any given register used as the
diff --git a/llvm/lib/Target/RISCV/RISCVRegisterInfo.td b/llvm/lib/Target/RISCV/RISCVRegisterInfo.td
index ab0d354967b34c7..98763a41b7caf3a 100644
--- a/llvm/lib/Target/RISCV/RISCVRegisterInfo.td
+++ b/llvm/lib/Target/RISCV/RISCVRegisterInfo.td
@@ -148,6 +148,8 @@ def GPRNoX0X2 : GPRRegisterClass<(sub GPR, X0, X2)>;
 // by tablegen.
 def GPRJALR : GPRRegisterClass<(sub GPR, (sequence "X%u", 0, 5))>;
 
+def GPRJALRNonX7 : GPRRegisterClass<(sub GPRJALR, X7)>;
+
 def GPRC : GPRRegisterClass<(add (sequence "X%u", 10, 15),
                                  (sequence "X%u", 8, 9))>;
 
diff --git a/llvm/test/CodeGen/RISCV/zicfilp-brind.ll b/llvm/test/CodeGen/RISCV/zicfilp-brind.ll
new file mode 100644
index 000000000000000..2f26d886b4d4438
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/zicfilp-brind.ll
@@ -0,0 +1,49 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 3
+; RUN: llc -mtriple=riscv64 -stop-after=finalize-isel < %s | FileCheck %s
+; RUN: llc -mtriple=riscv64 -mattr=+experimental-zicfilp -stop-after=finalize-isel < %s | FileCheck -check-prefixes=ZICFILP %s
+
+ at foo.arr = internal unnamed_addr constant [2 x ptr] [ptr blockaddress(@foo, %5), ptr blockaddress(@foo, %8)], align 8
+ at x = dso_local global i32 0, align 4
+
+define void @foo(i32 noundef signext %0) {
+  ; CHECK:   PseudoBRIND killed [[VAR:%.*]], 0
+  ; ZICFILP:   PseudoBRINDNonX7 killed [[VAR:%.*]], 0
+  %2 = sext i32 %0 to i64
+  %3 = getelementptr inbounds [2 x ptr], ptr @foo.arr, i64 0, i64 %2
+  %4 = load ptr, ptr %3, align 8
+  indirectbr ptr %4, [label %5, label %8]
+
+5:                                                ; preds = %1
+  %6 = load i32, ptr @x, align 4
+  %7 = add nsw i32 %6, 2
+  store i32 %7, ptr @x, align 4
+  br label %8
+
+8:                                                ; preds = %5, %1
+  %9 = load i32, ptr @x, align 4
+  %10 = add nsw i32 %9, 1
+  store i32 %10, ptr @x, align 4
+  ret void
+}
+
+define void @bar(i32 noundef signext %0) {
+  ; CHECK:   PseudoBRIND killed [[VAR:%.*]], 4
+  ; ZICFILP:   PseudoBRINDNonX7 killed [[VAR:%.*]], 4
+  %2 = sext i32 %0 to i64
+  %3 = getelementptr inbounds [2 x ptr], ptr @foo.arr, i64 0, i64 %2
+  %4 = load ptr, ptr %3, align 8
+  %t = getelementptr inbounds i8, ptr @foo.arr, i64 4
+  indirectbr ptr %t, [label %5, label %8]
+
+5:                                                ; preds = %1
+  %6 = load i32, ptr @x, align 4
+  %7 = add nsw i32 %6, 2
+  store i32 %7, ptr @x, align 4
+  br label %8
+
+8:                                                ; preds = %5, %1
+  %9 = load i32, ptr @x, align 4
+  %10 = add nsw i32 %9, 1
+  store i32 %10, ptr @x, align 4
+  ret void
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/68292