[GISel][RISCV] Legalize shifts with non-trivial shamt types

[dtcxzyw]

This patch widens the illegal shamt type i48 -> i64 to fix legalization failure: https://godbolt.org/z/4zMTnoW7h

[llvmbot]

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

@llvm/pr-subscribers-llvm-globalisel

Author: Yingwei Zheng (dtcxzyw)

Changes

This patch widens the illegal shamt type i48 -> i64 to fix legalization failure: https://godbolt.org/z/4zMTnoW7h

---

Full diff: https://github.com/llvm/llvm-project/pull/93019.diff

2 Files Affected:

• (modified) llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp (+2-1)
• (modified) llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-lshr-rv64.mir (+26)

diff --git a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
index c73fe2c6cecbe..606569caada23 100644
--- a/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
+++ b/llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp
@@ -137,7 +137,8 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
       .widenScalarToNextPow2(0)
       .clampScalar(1, s32, sXLen)
       .clampScalar(0, s32, sXLen)
-      .minScalarSameAs(1, 0);
+      .minScalarSameAs(1, 0)
+      .widenScalarToNextPow2(1);
 
   auto &ExtActions =
       getActionDefinitionsBuilder({G_ZEXT, G_SEXT, G_ANYEXT})
diff --git a/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-lshr-rv64.mir b/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-lshr-rv64.mir
index 8cbae0fa0173e..43318118f09c5 100644
--- a/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-lshr-rv64.mir
+++ b/llvm/test/CodeGen/RISCV/GlobalISel/legalizer/legalize-lshr-rv64.mir
@@ -336,3 +336,29 @@ body:             |
     PseudoRET implicit $x10
 
 ...
+---
+name:            lshr_i32_i48
+body:             |
+  bb.1:
+    liveins: $x10
+
+    ; CHECK-LABEL: name: lshr_i32_i48
+    ; CHECK: liveins: $x10
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x10
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 16
+    ; CHECK-NEXT: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK-NEXT: [[LSHR:%[0-9]+]]:_(s32) = G_LSHR [[TRUNC]], [[C]](s64)
+    ; CHECK-NEXT: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[LSHR]](s32)
+    ; CHECK-NEXT: $x10 = COPY [[ANYEXT]](s64)
+    ; CHECK-NEXT: PseudoRET implicit $x10
+    %1:_(s64) = COPY $x10
+    %0:_(s48) = G_TRUNC %1(s64)
+    %2:_(s48) = G_CONSTANT i48 16
+    %6:_(s32) = G_TRUNC %0(s48)
+    %7:_(s32) = G_LSHR %6, %2(s48)
+    %5:_(s64) = G_ANYEXT %7(s32)
+    $x10 = COPY %5(s64)
+    PseudoRET implicit $x10
+
+...

[arsenm]

LGTM, but IR tests are generally better

[tschuett]

For legalizer changes, MIR tests are preferable.

[arsenm]

For legalizer changes, MIR tests are preferable.

This was mostly useful for bringup and edge case handling, but overall MIR tests are harder to maintain and can miss the system not working as a whole