[RISCV] Support uimm32 immediates in RISCVInstrInfo::movImm for RV32.

[topperc]

This allows us to support larger stack offsets for FrameLowering.

Fixes #88365.

[llvmbot]

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

Author: Craig Topper (topperc)

Changes

This allows us to support larger stack offsets for FrameLowering.

Fixes #88365.

---

Full diff: https://github.com/llvm/llvm-project/pull/88464.diff

2 Files Affected:

• (modified) llvm/lib/Target/RISCV/RISCVInstrInfo.cpp (+9-2)
• (added) llvm/test/CodeGen/RISCV/pr88365.ll (+26)

diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp b/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
index d78f5bd9dedf3d..d2b3b69b98d34a 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
@@ -767,8 +767,15 @@ void RISCVInstrInfo::movImm(MachineBasicBlock &MBB,
                             bool DstIsDead) const {
   Register SrcReg = RISCV::X0;
 
-  if (!STI.is64Bit() && !isInt<32>(Val))
-    report_fatal_error("Should only materialize 32-bit constants for RV32");
+  // For RV32, allow a sign or unsigned 32 bit value.
+  if (!STI.is64Bit() && !isInt<32>(Val)) {
+    // If have a uimm32 it will still fit in a register so we can allow it.
+    if (!isUInt<32>(Val))
+      report_fatal_error("Should only materialize 32-bit constants for RV32");
+
+    // Sign extend for generateInstSeq.
+    Val = SignExtend64<32>(Val);
+  }
 
   RISCVMatInt::InstSeq Seq = RISCVMatInt::generateInstSeq(Val, STI);
   assert(!Seq.empty());
diff --git a/llvm/test/CodeGen/RISCV/pr88365.ll b/llvm/test/CodeGen/RISCV/pr88365.ll
new file mode 100644
index 00000000000000..73010fdf404473
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/pr88365.ll
@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s -mtriple=riscv32 | FileCheck %s
+
+define void @foo() {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addi sp, sp, -2032
+; CHECK-NEXT:    .cfi_def_cfa_offset 2032
+; CHECK-NEXT:    sw ra, 2028(sp) # 4-byte Folded Spill
+; CHECK-NEXT:    .cfi_offset ra, -4
+; CHECK-NEXT:    li a0, -2048
+; CHECK-NEXT:    sub sp, sp, a0
+; CHECK-NEXT:    .cfi_def_cfa_offset -16
+; CHECK-NEXT:    addi a0, sp, 4
+; CHECK-NEXT:    call use
+; CHECK-NEXT:    li a0, -2048
+; CHECK-NEXT:    add sp, sp, a0
+; CHECK-NEXT:    lw ra, 2028(sp) # 4-byte Folded Reload
+; CHECK-NEXT:    addi sp, sp, 2032
+; CHECK-NEXT:    ret
+  %1 = alloca [1073741818 x i32], align 4
+  call void @use(ptr %1)
+  ret void
+}
+
+declare void @use(ptr)

[wangpc-pp]

LGTM.

[wangpc-pp]

Is this right?

[topperc]

I don’t think it is.

[topperc]

It is correct. The stack offset needs to be 0xfffff800 as an unsigned number. Which is -2048.