[RISCV][GISel] Use default lowering for G_DYN_STACKALLOC.

Author: topperc

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

@@ -191,6 +191,8 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST) {
 
   getActionDefinitionsBuilder({G_MEMCPY, G_MEMMOVE, G_MEMSET}).libcall();
 
+  getActionDefinitionsBuilder(G_DYN_STACKALLOC).lower();
+
   // FP Operations
 
   getActionDefinitionsBuilder({G_FADD, G_FSUB, G_FMUL, G_FDIV, G_FMA, G_FNEG,

llvm/test/CodeGen/RISCV/GlobalISel/legalizer/rv64/legalize-dyn-alloca.mir

@@ -0,0 +1,40 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -mtriple=riscv64 -mattr=+d -run-pass=legalizer %s -o - \
+# RUN: | FileCheck %s
+
+---
+name:            test_simple_alloca
+body:             |
+  bb.1:
+    liveins: $x10
+
+    ; CHECK-LABEL: name: test_simple_alloca
+    ; CHECK: liveins: $x10
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x10
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 4294967295
+    ; CHECK-NEXT: [[AND:%[0-9]+]]:_(s64) = G_AND [[COPY]], [[C]]
+    ; CHECK-NEXT: [[C1:%[0-9]+]]:_(s64) = G_CONSTANT i64 15
+    ; CHECK-NEXT: [[ADD:%[0-9]+]]:_(s64) = nuw G_ADD [[AND]], [[C1]]
+    ; CHECK-NEXT: [[C2:%[0-9]+]]:_(s64) = G_CONSTANT i64 -16
+    ; CHECK-NEXT: [[AND1:%[0-9]+]]:_(s64) = G_AND [[ADD]], [[C2]]
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:_(p0) = COPY $x2
+    ; CHECK-NEXT: [[PTRTOINT:%[0-9]+]]:_(s64) = G_PTRTOINT [[COPY1]](p0)
+    ; CHECK-NEXT: [[SUB:%[0-9]+]]:_(s64) = G_SUB [[PTRTOINT]], [[AND1]]
+    ; CHECK-NEXT: [[INTTOPTR:%[0-9]+]]:_(p0) = G_INTTOPTR [[SUB]](s64)
+    ; CHECK-NEXT: $x2 = COPY [[INTTOPTR]](p0)
+    ; CHECK-NEXT: [[COPY2:%[0-9]+]]:_(p0) = COPY [[INTTOPTR]](p0)
+    ; CHECK-NEXT: $x10 = COPY [[COPY2]](p0)
+    ; CHECK-NEXT: PseudoRET implicit $x10
+    %1:_(s64) = COPY $x10
+    %0:_(s32) = G_TRUNC %1(s64)
+    %2:_(s64) = G_ZEXT %0(s32)
+    %5:_(s64) = G_CONSTANT i64 15
+    %6:_(s64) = nuw G_ADD %2, %5
+    %7:_(s64) = G_CONSTANT i64 -16
+    %8:_(s64) = G_AND %6, %7
+    %9:_(p0) = G_DYN_STACKALLOC %8(s64), 1
+    $x10 = COPY %9(p0)
+    PseudoRET implicit $x10
+
+...