[GISel][RISCV] Legalize shifts with non-trivial shamt types (#93019)

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

Author: dtcxzyw

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp

@@ -141,7 +141,8 @@ 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})

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
+
+...

llvm/test/CodeGen/RISCV/GlobalISel/shift.ll

@@ -0,0 +1,48 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=riscv32 -global-isel -global-isel-abort=1 -verify-machineinstrs < %s 2>&1 | FileCheck %s --check-prefixes=RV32
+; RUN: llc -mtriple=riscv64 -global-isel -global-isel-abort=1 -verify-machineinstrs < %s 2>&1 | FileCheck %s --check-prefixes=RV64
+
+define i16 @test_lshr_i48(i48 %x) {
+; RV32-LABEL: test_lshr_i48:
+; RV32:       # %bb.0:
+; RV32-NEXT:    srli a0, a0, 16
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: test_lshr_i48:
+; RV64:       # %bb.0:
+; RV64-NEXT:    srliw a0, a0, 16
+; RV64-NEXT:    ret
+  %lshr = lshr i48 %x, 16
+  %trunc = trunc i48 %lshr to i16
+  ret i16 %trunc
+}
+
+define i16 @test_ashr_i48(i48 %x) {
+; RV32-LABEL: test_ashr_i48:
+; RV32:       # %bb.0:
+; RV32-NEXT:    srai a0, a0, 16
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: test_ashr_i48:
+; RV64:       # %bb.0:
+; RV64-NEXT:    sraiw a0, a0, 16
+; RV64-NEXT:    ret
+  %ashr = ashr i48 %x, 16
+  %trunc = trunc i48 %ashr to i16
+  ret i16 %trunc
+}
+
+define i16 @test_shl_i48(i48 %x) {
+; RV32-LABEL: test_shl_i48:
+; RV32:       # %bb.0:
+; RV32-NEXT:    slli a0, a0, 8
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: test_shl_i48:
+; RV64:       # %bb.0:
+; RV64-NEXT:    slliw a0, a0, 8
+; RV64-NEXT:    ret
+  %shl = shl i48 %x, 8
+  %trunc = trunc i48 %shl to i16
+  ret i16 %trunc
+}