[RISCV][GISel] Support fp128 arithmetic and conversion for RV64.

We can support these via libcalls in libgcc/compiler-rt or
integer operations for fneg/fabs/fcopysign. fp128 values will
be passed in two 64-bit GPRs according to the psABI.

Supporting RV32 requires sret which is not supported by libcall
handling in LegalizerHelper.cpp yet. It doesn't call canLowerReturn.

Author: topperc

llvm/include/llvm/CodeGen/GlobalISel/LegalizerInfo.h

@@ -778,6 +778,11 @@ class LegalizeRuleSet {
   LegalizeRuleSet &libcallFor(std::initializer_list<LLT> Types) {
     return actionFor(LegalizeAction::Libcall, Types);
   }
+  LegalizeRuleSet &libcallFor(bool Pred, std::initializer_list<LLT> Types) {
+    if (!Pred)
+      return *this;
+    return actionFor(LegalizeAction::Libcall, Types);
+  }
   LegalizeRuleSet &
   libcallFor(std::initializer_list<std::pair<LLT, LLT>> Types) {
     return actionFor(LegalizeAction::Libcall, Types);

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

@@ -491,21 +491,23 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
 
   // FP Operations
 
+  // FIXME: Support s128 for rv32 when libcall handling is able to use sret.
   getActionDefinitionsBuilder(
       {G_FADD, G_FSUB, G_FMUL, G_FDIV, G_FMA, G_FSQRT, G_FMAXNUM, G_FMINNUM})
       .legalFor(ST.hasStdExtF(), {s32})
       .legalFor(ST.hasStdExtD(), {s64})
       .legalFor(ST.hasStdExtZfh(), {s16})
-      .libcallFor({s32, s64});
+      .libcallFor({s32, s64})
+      .libcallFor(ST.is64Bit(), {s128});
 
   getActionDefinitionsBuilder({G_FNEG, G_FABS})
       .legalFor(ST.hasStdExtF(), {s32})
       .legalFor(ST.hasStdExtD(), {s64})
       .legalFor(ST.hasStdExtZfh(), {s16})
-      .lowerFor({s32, s64});
+      .lowerFor({s32, s64, s128});
 
   getActionDefinitionsBuilder(G_FREM)
-      .libcallFor({s32, s64})
+      .libcallFor({s32, s64, s128})
       .minScalar(0, s32)
       .scalarize(0);
 
@@ -521,19 +523,22 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
       .legalFor(ST.hasStdExtD(), {{s32, s64}})
       .legalFor(ST.hasStdExtZfh(), {{s16, s32}})
       .legalFor(ST.hasStdExtZfh() && ST.hasStdExtD(), {{s16, s64}})
-      .libcallFor({{s32, s64}});
+      .libcallFor({{s32, s64}})
+      .libcallFor(ST.is64Bit(), {{s32, s128}, {s64, s128}});
   getActionDefinitionsBuilder(G_FPEXT)
       .legalFor(ST.hasStdExtD(), {{s64, s32}})
       .legalFor(ST.hasStdExtZfh(), {{s32, s16}})
       .legalFor(ST.hasStdExtZfh() && ST.hasStdExtD(), {{s64, s16}})
-      .libcallFor({{s64, s32}});
+      .libcallFor({{s64, s32}})
+      .libcallFor(ST.is64Bit(), {{s128, s32}, {s128, s64}});
 
   getActionDefinitionsBuilder(G_FCMP)
       .legalFor(ST.hasStdExtF(), {{sXLen, s32}})
       .legalFor(ST.hasStdExtD(), {{sXLen, s64}})
       .legalFor(ST.hasStdExtZfh(), {{sXLen, s16}})
       .clampScalar(0, sXLen, sXLen)
-      .libcallFor({{sXLen, s32}, {sXLen, s64}});
+      .libcallFor({{sXLen, s32}, {sXLen, s64}})
+      .libcallFor(ST.is64Bit(), {{sXLen, s128}});
 
   // TODO: Support vector version of G_IS_FPCLASS.
   getActionDefinitionsBuilder(G_IS_FPCLASS)
@@ -546,7 +551,7 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
       .legalFor(ST.hasStdExtF(), {s32})
       .legalFor(ST.hasStdExtD(), {s64})
       .legalFor(ST.hasStdExtZfh(), {s16})
-      .lowerFor({s32, s64});
+      .lowerFor({s32, s64, s128});
 
   getActionDefinitionsBuilder({G_FPTOSI, G_FPTOUI})
       .legalFor(ST.hasStdExtF(), {{sXLen, s32}})
@@ -558,7 +563,8 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
       .widenScalarToNextPow2(0)
       .minScalar(0, s32)
       .libcallFor({{s32, s32}, {s64, s32}, {s32, s64}, {s64, s64}})
-      .libcallFor(ST.is64Bit(), {{s128, s32}, {s128, s64}});
+      .libcallFor(ST.is64Bit(), {{s32, s128}, {s64, s128}}) // FIXME RV32.
+      .libcallFor(ST.is64Bit(), {{s128, s32}, {s128, s64}, {s128, s128}});
 
   getActionDefinitionsBuilder({G_SITOFP, G_UITOFP})
       .legalFor(ST.hasStdExtF(), {{s32, sXLen}})
@@ -579,7 +585,8 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
       // Otherwise only promote to s32 since we have si libcalls.
       .minScalar(1, s32)
       .libcallFor({{s32, s32}, {s64, s32}, {s32, s64}, {s64, s64}})
-      .libcallFor(ST.is64Bit(), {{s32, s128}, {s64, s128}});
+      .libcallFor(ST.is64Bit(), {{s128, s32}, {s128, s64}}) // FIXME RV32.
+      .libcallFor(ST.is64Bit(), {{s32, s128}, {s64, s128}, {s128, s128}});
 
   // FIXME: We can do custom inline expansion like SelectionDAG.
   // FIXME: Legal with Zfa.